The guitarist I play with has one that he uses with a Fender. It's the right impedance model (when you buy a Hot Plate, you buy the one that matches the load your amp expects) for my F-50, so we tried it one day, just to see what it sounded like. I think it's useful to run the amp in its sweet spot, with light attenuation so the volume isn't quite as horrific, but doesn't sound all that great with the amp running full-tilt and the attenuator at higher settings -- the Hot Plate definitely sucks tone, it isn't too noticeable at lower settings, but it's very apparent at higher attenuation.
Attenuators are neat, I guess, and I can see where they'd be useful for a lot of people, but I don't think I'd ever use one, as I prefer to keep my rig simple.