I've owned two of them. The first one I ran into the Blue channel (set on Plexi mode) of my XTC Classic and it was awesome. Nailed those early VH tones. Now that I no longer have the XTC, the second one is still trying to find it's spot. The Plexitone definitely prefers a clean to hairy amp signal, with the pedal doing all the rest. For a boost to add some punch and hair, I MUCH prefer my OCD.
But if you're looking for a fly-gig pedal that you could count on being able to get some great rock tones, even if they had you running into a backline with Fenders or Roland JC120 amps, the Plexitone would be hard to beat. I A/B'd it against an early Radial Hot British and they were very close. I may have very slightly prefered the Radial tonewise, but the features on the Plexitone (solo boost and two channels) beat the Radial so it got returned to the store.
I also used to play my Plexitone through my Fender Twin reverb and it sounded really good. I ran into a Radial ABY, then out of the ABY, then out of the A side of the Y pedal into the PT and then into one channel set on dark. And then out of the B side of the Y pedal straight into the other channel set on bright for cleans. Then I could just switch back and forth between channels using the ABY pedal and it was like having a great switcher. I could have lived and gigged with that setup just fine for classic rock, country, etc. But the XTC still spanked that setup for those genres and more so that's why I sold it all.