Had a chance to play with the 10-18 STM on the EOS-M this past weekend. Very balanced weight for the M and nice auto focusing speeds (similar to 50-255 STM and 18-55 STM, faster than 22 STM).
I was on the fence until I tried it out, preordered the lens yesterday. I spent quite a bit on the adapter already, so while the mtf doesn't look as good as the 11-22, i figure cheaper cost and the extra 1mm is worth it.
Looks quite sharp wide open, the shot was taken with (10mm - f/4.5 - 1/30 - ISO 1000). Definitely need to try it out in the field to be sure, will report back once I get the lens.