I've owned the Roland KC-500 and was quite disappointed with it. I've read lots of reviews and opinions from other keyboardists on portable amps, and I'm excited about this new product by Hartke, which has gotten the type of feedback I've been hoping for when I get ready to buy again.
Read on the Sweetwater site, a recent buyer's review:
best thing is look for a small pa type setup... ya gotta realize that we can go lower than a bass and higher than cymbals... so it takes a pretty good speaker and more power than a guitar ever needed...