I have one. I used to use it before I started getting it worked on. I think it's a great-sounding amp, and they have a lot of features. If it's in good shape, buy it. Don't be afraid to play it loud in the store and ask lots of questions. They're two ohms, also, which is a pretty cool feature. I'd also download the manual on this site.
Coliseum 300's in good working order aren't something you see a lot of these days.