I wouldn't say they are rare, Gibson makes them every year, I think MF is blowing out the 2016s for like $1100. I had one, it was cool and surprisingly light, but the headstock tended to dive if you took your hand off it and just let the strap support the weight
I dig the Firebirds. They're pretty widely used imho. Cid is right in that they are heavily discounted on closeout and - with nylon straps like the SG to some extent - the headstock tends to drop due to the weight/shape but so did my AR2000 before moving the strap pin from the upper horn to the body rear. It's just that many here would pay $1500 for an indo premium jem over $1100 for USA made Firebird neck-thru.