| I borrowed a KC-300 (100 watts, 12" + horn) from a keyboardist friend a couple months ago. I was thinking of buying it as an around-the-house/small gig amp for both DB and BG.
At low volumes it sounds good--full sound from top to bottom. It has 4 input channels and a master 2-band EQ. Bass guitar sounded fine either plugged straight in or through a SansAmp Bass Driver/DI. I ran my Messenger DLX EUB and New Standard Cleveland with Bass Max and Schertler Stat-B pickups through it. I found that if I didn't roll off the lows considerably (with either the onboard tone control or Fishman Platinium Bass EQ's low-cut filter) the speaker would crap out pretty quickly, and you could hear air chuffing out of the small port. That said, it performed respectably at a coffeehouse jazz trio gig.
I was more impressed with it as an all-purpose at-home rig, with its headphone jack, mixer, and impressive in/out section. It would also be good for a teacher--you could hook up a couple of basses and a CD player or drum machine, or you could use it as a mini-PA for cafe gigs. It was worth it for $200 used but I didn't really need it.
IMO the larger version (KC-500) with 15" speaker sounds horrendous--boomy lows, unnatural mids, plus it's pretty big and heavy. | 
