I use mine with one of my bands... great classic rock tones.
Regarding mods - I have a few for them - one is the standard clarity/warmth mod I do on dang near all the modules I get ahold of, another is plexi-specific that allows more mids. It just makes the mids on 5 the same as a stock one on 10 - so you can get more if you need it. The plexi module IMHO sounds better with more midrange - much crunchier. I can also gain them up a little bit, but too far and you might as well just buy a brown.
JTM is a cool sounding module too, but it's much looser than a plexi. Stock, I think of the plexi module as Led Zep and the JTM as more of a Neil Young vibe.
Pete