I'm currently using this for a Marshall 100W model 1959 Plexi and a 100W JCM800 2203X.
As a recording device:
The speaker and microphone simulation, as well as the built in effects are excellent. But the box is missing a balanced line out to round out the package.
As an attenuator/load box:
Works very well when playing with no speaker attached over headphones, provided you have some good headphones.
Unfortunately when using the speaker the sound is severely muffled with normal bass but greatly diminished mids/highs. And there are only 5 volume options due to a stepped knob controlling the speaker output.
Overall a quality piece of equipment, but lacking the last few features that would make it truly great.