A couple of years ago I picked up a 300/500 Schneider Symmar for $200 at a camera show. I had always heard the convertibles were dogs but this appeared to be new, and I was thinking more of the Copal #3 shutter and what I could use it for.
At 300 the lens is pretty sharp and very good when stopped down. The 500mm seems to be a little bit soft. It works for some portrait situations and certain landscapes. It is big and heavy. Since then I have bought other standard lenses to cover that range and are small enough to be easily used on a smaller 4x5 lens board.