Have owned 2 of the original versions, as I lost one in VN in a taxi boot, and the current mark 2 version.

Been using them for speciality work shots for maybe 4 years or more. The first ever one I had was sharp, 2nd one not so great on the 5D2, but when switched over to the 5D3 I noticed a big lift in overall sharpness.

However, the current mark 2 version, is very sharp and a drastic improvement on all levels from the first model.