Each version upgrades something! Obvious or why do it? As new lenses are added to the Canon line, updates in the extenders is required. How much better is for you to decide. I have the second version and do not intend of getting the third version.
Canon has a list as to which converter works or recommended for each lens. You know if you got the lens form or in Japan it is not a Canon USA version? DId you get a grey market lens?
EB
EOS 1DX and 1D Mk IV and less lenses then before!
