The disadvantage of non-usm is that it isn't usm.


All of canons best af lenses are usm, it is faster and quieter than "conventional" motors for af.


I've never used the non-usm version of the macro, but I would guess that is true in this case, too.


When I was buying, the price difference was modest, so I went with the usm. If I had it to do over again, I would get usm even if the price difference was substantial.