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.
Good advice it1....I had one. Bought it new in 86. Decent little bike & pretty comfortable. I think it made something like 60hp. New they went for right around 2K. The biggest problem I see is it's a 26 yr old bike now & parts & tires (16" rims) might be a problem. You would probably be better off spending a couple more bucks on the front end & getting something more modern. But If they're giving it to you, what the heck.