I don't know anything about the A-2 model but I have a B model. I read so many contradicting reviews about the Model B.
The model B is great, it fits on my New F-1 (I read somewhere that it won't but it does). With the adapter "S" it will fit on my A-1, AE-1 program, Rebel T3i, EOS 1v and 5D mark II.
Hope this info helps.