It is difficult to argue that a rotary is inherently better when one looks at what is often considered the most flexible machine currently offered, the Decent' does it with a pair of vibe pumps. Vibe pumps cost much less, flow much less, are noisier, have quite severe limits on run time and conceptually don't last as long. Unless you need instant 9 bar, there should be no particular advantage of one over the other in the quality of espresso produced. At least in my machine the pump flows more water than necessary for a shot and is capable of enough more pressure than 9bar that the pressure relief seems to keep the pressure at the puck constant, even with the elements cycling.

But a rotary pump is quieter, so it's used in upscale home machines, I assume mostly for noise reduction.

A rotary also makes the initial filling of the boiler(s) easier as there is no need to do the minute on/minute off dance, a rotary pump should be able to run almost continuously, depends on the motor rating.

Ira

But a rotary pump is quieter, so it's used in upscale home machines, I assume mostly for noise reduction.

I've looked at a few recently and would not say they were much quieter than my machines. They have a different sound, and some with pressure profile sound distinctly odd.

As far a the noise goes, you also have to also think about the over all build of the full machine. I just went from a Breville Pro to an ECM Synch. The Breville is full plastic and that vibe pump connected to the thermoblock was pretty loud and when you have it sitting next to the tank of an ECM Synch with well designed motor mounts there is a huge difference. But if you had a very well designed and built machine with vibe pump next to the ECM Synch, how much difference would there be? I bring this up because if you do have a very well built vibe pump machine and drop a good chunk of cash to upgrade to a machine with a rotary, if sound is the only reason I don't know how happy you are going to be with the investment.

For me personally, I went with rotary as part of the overall package. It was one of the check boxes on my list of why to buy a machine. If I could have gone with a Profitec Pro 600 with joystick valves and anthracite panels for $600 less than the ECM Synch, I may have went that way. For me I don't think the pump alone was worth the jump up to the Synch, but all of the difference together plus the rotary pump is why I went that way...plus my wife liked the look of the Synch and once she gave me the green light was I ever really going to go for a cheaper machine.