I think thatīs one of the more ugly lens,whith a little glass but its optical quatity is fantastic. Yes, its AF is noisy and slow but for my usually photo at this focal leng I donīt need fast AF.
I test this lens with the canon 50mm f/1,4 and 24-105 L. Between 24-105 and 50mm f/2,5 this macro lens beat in over apertures at 24-105 L series.
Between 50mm f/1,4 and 50mm f/2,5 in the middle allways is better macro lens, but in the corner 50mmf/1,4 lens is best to f/3,6 equal at f/4 and worst from f/5,6."This test is only valid with a full frame camera".If you had crop camera and don,t need extra aperture this is your lens.
I usually donīt use this lens for macro becouse I had 100mm macro, but if you need more than 1:2 use kenko extend tubes with 50mm f/2,5 you can get very good result.
Itīs one of more sharp lens I had, similar canon 200mm f/2,8L