Re: crate powerblock
The appeal of them was that they can get used pretty transparaently by a modeler. I bought mine and used it with a Marshall 2 x 12 cab and a Line 6 PodXT. Setting it up in one of the inputs removes all of the color that the unit puts into the sound; think of it as having two modes, one of which colors the tone to be tube-like and the other to NOT have the coloration.
With it coloring the result was decent, but not great. It would work in a pinch, but I wouldn't want to be married to it for the whole night of a three-set bar gig unless I totally had to.
Without the coloring there was slightly less output but the effect was quite good. It did require tweaking of the PodXT patches to match it, but I would of expected to have to do that for different cabs, never mind different power amps. I tweaked together three different sounds, a Plexi, a high-gain and one that was kinda muddy (that was the effect I was going for). I spent most of the time playing the Plexi and I have to admit that it was actually quite good. I got alot of compliments on my tone.
I wouldn't really consider the PowerBlock for a practice amp. It seems kind of limited in deference to something like a Pod. But it does have that option, I just can't really evaluate it.
The one thing folks rarely mention is that the silly thing has a 5 year warranty on it. Not bad all in all if you're going to haul it to gigs even as a backup.