The Radian was a parts-bin bike built to a price to get sales in a tough bike economy. It was a pretty good bike for its day. The forum / aftermarket support is a bit weak, and plastics are hard to find. There is a forum/newsletter/newsgroup at badrad600.com .
I helped a friend pick one up recently, and underestimated the amount of time and cost to get it into operating condition. On any bike that old, you need to check plastics, compression, charging system, fuel tank (rust, etc), rotors, any signs of abuse, etc. If the bike is in perfect/excellent condition, you s/b okay. It is a very pleasant bike, but again, support is limited. You s/b fine on consumables, but parts could be problematic.