EDIT : IIRC, the boiler comes set much higher than 200°F, more like 220°F
I have both a Vibiemme Domobar Super HX w PID and DoubleDomo PID.
As with any DB, there is a delay between adjusting the boiler temperature and the shot. You can adjust the shot temperature but flushing a LOT of water through the DB, but it makes no sense.
An HX is more flexible in adjusting the temperature, but at the expense of time. That being said, if you flush an HX down, you have to wait a bit for it to recover if you want to brew hotter on the next shot on a short interval.
If you want to change coffee on a shot by shot basis, get an HX. If you change coffee infrequently, either will suffice.
There's not a huge difference in water usage. I use about 1L / day for 3-4 singles on either machine.
See
HX espresso machines waste water - or do they?