I'm very, very impressed with mine. I'm in the early stages of an informal review and comparison to the Bezzera Strega. I've never pulled shots from a Pompeii but there's some excellent forum members who've had many years of experience with their's and they'll likely chime in. AFAIK, the extraction dynamics are the same as long as the version of the groups are the same.

Very anecdotally, I find a very obvious difference between the Leva and the Strega. The Strega by its hybrid design works to extract the high notes of bright coffees well. It's powerful 11bar of gentle vibe pump pre-infusion allows for more challenging light roasts to be extracted. But I'm finding that I'm drawn to the Leva shots more. The extraction flavors really enhance the pleasant mid-tones and seem to extend them further. Shots are softer, smoother and even sweeter, without crumbling into plain comfort food blend territory.

Build wise, I'll mention some drawbacks with the Leva, then some positives. Drawbacks are the 54mm baskets, needing a new tamper. I'm in the process of working with IMS on a project there. The Leva is very, very unforgiving of technique. Dose and grind live on a razors edge, but when nailed, I get shots I've never had before on the Strega ( I can run the Strega without a pump and essentially "match" the effects of a classic Italian lever and it still doesn't trump the Leva).

The Leva's screen is held in place by a circlip that isn't fun to remove or replace. I find that when flushing, I get a jet of water that sorta dog-legs it to the side because the water hits the obstructing ears of the circlip and deviate the flow a bit. I highly doubt this makes any difference when there's a puck in there however, so I'm not too worried yet about the extractions.

The Leva is a massive group mounted to a smaller, home friendly box. This results in a shorter space from drip tray to the bottom of the stock portafilters spouts. I had a buddy with a lathe turn one into a bottomless portafilter and I'm very happy with the results. The added inch or so of space is quite nice in an otherwise cramped space. The portafilters on LSM groups are some of the densest I've ever seen. Almost a 1/4" thick on the base. My machinist friend was surprised by how thick it was.

On the Leva, the first time you dose too high with too fine a grind you'll likely explode the portafilter off the group. That's a loud, scary mess to clean up. I'm finding it behaves it's best with more traditional dosing and grind settings for classic levers (traditional Gaggia, etc). Extraction with the Leva are effected strongly by the basket size, since your shot size is also determined by the water space above the puck. It was interesting to note over the weekend that the single basket it comes with is essentially unusable. I dosed less than 7 grams of coffee and it still was expanding up into the shower screen and extracting poorly. Looking at the spent pucks in the basket, there's a cracked circumferential ring where the high inner shoulders reduce the depth of the coffee bed. I'm sure if I ground finer and finer and played with it long enough, I'd land at something appropriate but I haven't bothered to pursue the single basket much since the first few attempts.

I'm currently a bit ambivalent about the PID design. On the plus side, you can sorta think about it as a very quick and easy to reach Pstat that you can adjust easy on the fly for temp changes, but it's not that simple, there's more to it than that. Dropping the temp low for darker roasts to avoid harshness, bitterness or the dreaded robusta burned tire aroma should you be pulling classic espresso blends thru the machine (and you should) also greatly affects your steaming strength. I must admit that I have never disciplined myself to master latte art or executed regimented flawless steaming technique. It will still steam well enough at lower PID settings but it takes longer and I haven't disciplined myself to master either form yet.

The PID isn't even advertised by the vendors of the machine as a shot tuning/extraction feature. It's only mentioned in regards to steaming functionality. These massive brass groups (and the LSM is one of the biggest ever made) are exquisitely temp stable, very well engineered and don't tend to require much mucking around with. It's a 35 pound brass radiator exposed to ambient air. The heat dynamics of the shot's water cooling as it moves thru the group as it passes through a coffee bed are probably far more evolved than what meets the eye. Again, I think it harkens back to the point that these Italian engineers knew what they were doing, with decades and decades of trial and error and refinement. They didn't have PID technology on their groups back then and they still managed to please their customer base.

I'm in the process of building a thermofilter with EricS's help and will have more data later on. The flow dynamics during the actual shot must be exactly replicated on a thermofilter in order to understand the heat shedding dynamics of the group better. I've mounted my pressure gauge to one of the spare portafilters and have noted about 8.5 bar pressure from the dual springs throughout the shot. The pressure doesn't tail off quite the same as other spring levers, but rather, seems to hold steady until there's almost no more water left to push thru. More investigation on that is ongoing though. Pre-infusion is boiler pressure obviously.

On the upside (and they are many and significant), the build quality makes the Strega blush in comparison. very sturdy build, thick gauge wiring, very thick boiler insulation. Absolute dead silent operation. The only sound the machine makes is when the boiler refill Gicar controller opens to let water in. On the Strega, you can hear the element as it boils the water. Nary a peep out of the Leva. The Leva will likely outlive the Strega with ease. The PID's if they fail can be replaced and many vendors stock them. That's the only tech-y bit of the Leva. Everything else is pared down and simple. No pump, minimal parts to service. It is very well built and will be quite easy to maintain.

The Leva makes flushing the boiler a very simple 3 minute task and you don't even have to power off the machine. I've done it with both the power off and on. The PID controlled element shuts off if the boiler level is low during refilling, so you can take the fully heated machine, turn it off, open the hot water tap and drain almost the entire boiler in just over 2 minutes.

Steaming on the Leva is obviously on par with quality commercial gear. It comes with four different tips to choose from. I'm currently working on switching out to a joystick steam wand because I still prefer those to rotary valves and I hate the sound of the springs scratching and rubbing as they turn.

Extractions on the Leva, like mentioned previously here in this reply are extremely good. I'd say objectively better than the Strega by a hair. Subjectively much better if you like softer shots. Like I said before, the middle tones are so much more well rounded and enhanced versus the Strega. Shot profiling is just as easy on the Leva, there's ample room to explore any coffee.

The Leva also gives a very confident feel in the hands of the user. The group is so solidly mounted to the frame and boiler that it all feels like one solid piece of metal. Nothing flexes at all. It's very very fun to use. And it's an absolute joy how quiet it is. I haven't dusted off my HG-One in quite some time, but I imagine the stealth shot magic would be quite nice.

More to come, but it will be a while.

Lever pull effort on the Leva is much easier. There is more total length on the Leva's armature from it's pivot point which should play a role. Plus, the Strega as you pull, doesn't rotate on a center axis, it rolls on cams along a path. Both create a different feel and both alter extraction, but as to extraction, it's hard to nail down specifics. It's likely anecdotal.

The feel is completely different between the two as well. With the Strega, when you back off the pump, the spring catches and pulls very hard immediately (think "knock your teeth out if you're stupidly in the wrong place, using it wrong") whereas on the Leva, it's a gentle release that you can practically guide with your fingertips, it's neither apt to snap back down or fly back up. It doesn't pick up that powerful momentum until it's rotation has exceeded a certain point in it's arc. That doesn't mean I'd just let it fly, but it's easier to guide out of that jaw shattering danger zone. I might even be able to get my fiancé to start pulling shots with it. Then I'm on easy street.

I should emphasis that most of my measurements are not nailed down yet. I expect higher spring pressure and a more tapered end to the pressure in normal use and practice with my gauge. A homemade portafilter pressure gauge doesn't take into account the gradually reducing resistance of the puck as the coffee extractables are removed, so you should see less resistance and lower pressure for a given flow ( or just an increase of flow towards the tail end) there should be a bit of Poiseuille's Law in effect to keep in mind. This group has the same strength of groups like the Bosco/L1 (perhaps stronger being double sprung) and a narrower radius outlet. The perceivable extraction notes should be different.

A nice thing about the Leva is there's more clearance away from the faceplate of the machine, I had to do all sorts of tweaks to get my gauge to fit under the Strega. No problems at all with the Leva. And with probably close to 3 liters of water in a 5 liter boiler, with tons of mass (heat retention) you can pull measurement after measurement after measurement, tweaking the needle valve to adjust flow to your hearts delight.

Other things: I'm left handed, so I don't like having the steam wand on the right side. You righty's might actually really like that though.

The steaming tray on top is a lot of fun. I don't leave it on, you can have an entire rack full of cups toasty hot in about 30 seconds or so. I pull a good deal of my shots right into room temp cups, or I flush into the cup, dump and wipe clean, just to warm it a touch and to make sure there isn't anything but crystal clean ceramic to pull into.