Ahh...Yes...Well...
I have the Mk III version and I found it to be awful in comparison to Guitar Rig 5, TH2 or Amplitube 3 (and that was disappointing too).
Just dull, raspy and lifeless. Nothing sounded inspiring.
No sparkle could be dialled in, and no convincing hi gain tones that sounded anything like my own real-world amps.
It certainly didn't sound like that promo video.
It may be that they are faithful representations of the amps and effects it simulated (I have never personally owned them).
But if so, I wouldn't buy any amp or module based on the ReValver Mk III sim.
Changing valves in the "Unique Selling Point" section of ReValver Mk III just made awful sims sound a slightly different shade of awful.
Admittedly, I didn't really put the work in (it's just that bad) and left it gathering digital dust relatively quickly.
I've stuck with Guitar Rig 5 (my personal winner).
To compete against the competition now, ReValver Mk IV will have to have improved massively.
Please tell me this is so!