FD/EF adapters on Ebay

Has anyone bought a FD/EF adapter off Ebay? I'm kicking around getting one for my Canon 500mm mirror lens but I've heard some mixed reviews about them. Since the trip I wanted to use the lens on is this week, I won't be buying it for a while, (Speedlite 430EX and the 28-135 IS lens are next on my list). Just looking for some thoughts on the adapters.

The general consensus is that the only worthwhile FD->EOS adapter worth getting is the expensive official Canon one. The generic ones are quite simply crap and make a huge difference to the IQ.

I got one for exactly the same thing you are looking for - my 500 mm FD Mirror - it does allow the lens to work, but I have yet to be satisified with a single shot - too blurry. I've shot under full sun - tripod (500mm..duh!) and still don't like the results - if I want a fairly low resolution 'snapshot' its okay, but don't expect the same quality you get with a AF lens. BTW - got very good shots when I used it on a T90 and AE1

A teleconverter for your 75-300 is probably a better choice. Thats all the FD-EF mounts really are.