I never owned one thank God but I had the misfortune of having to play through a Peavey Mark IV through a Peavey 2 x 15" cab several times. Talk about a lousy non descript tone. They seem to be common around here or were and I ran into them a lot unfortunately.
I saw scads of those Mark heads in the Midwest long, long ago. Oddly enough, I never played one nor did my peers own them. I was seeing them as trades in music stores and with dust on them in pawn shops