While using the 90mm Macro-Elmar-M (MEM, for short), I find it a bit fiddly to make sure the hood is on, aperture set right, and the lens properly extended and lock in place. However, once that's done, it's all smooth sailing. Comparing to the 90mm Elmarit-M, I find the color rendering a little different, more accurate, I think. The 90mm Elmarit-M seems to have its own signature and is more prone to flare. The 90MEM, on the other hand, shows things as they are and it's easier to carry around. Comparing to the photo from the 90mm Elmarit-M [HERE], I think you'll see some subtle differences in the images.
The girls from next door joined us at the end, giving me more excuses to shoot some more.