For what they are they aren't bad. They do the bedroom practice situation quite fine. But, Marshall didn't exactly become what they are today by making SS amps.

I've never A/B'ed a bunch of SS amps, but I have played a few SS Marshalls, and they were generally on par with SS Fenders.
However, if I were buying another practice amp I'd probably buy a Line6 combo. A buddy of mine owns a spider and if you spend the time to really tweak them they can roduce better tones than just about any similarly priced SS amp, especially with a speaker change (the stock drivers in those spiders are junk, which I think is why they get such a bad rap).