The Rumbles really aren't that bad at all. If you don't try to turn them up stupid loud, they are pretty decent sounding amps. I play through my singer's 1x8 15w rumble combo at his place when we do writing and it sounds pretty boss for a 1x8 combo lol.
Just mind your volume and how hard you are pushing the head/cab. I'd put them on par with or better than the GK Backline/Goldline stuff. They aren't an all-tube stack or stupid loud fEarful cab, but they aren't supposed to be. They'll get you through rehearsal and some gigs, no shame in something that gets the job done at a modest price.