I would not buy the adapter because I don't see the point in having a big lens on a tiny body it's past the point where it's light to carry easy to slip into a small case.
The EF adapter allows the M to serve as a backup body when traveling with a bag full of lenses that would otherwise become useless if the primary camera fails. When traveling, I bring the M + 22 along for times when small size is necessary, and the EF adapter 'just in case'.
+1 on using it as a backup body. I keep one with adapter and the 50mm 1.8 for low light along with both eos-m lenses in a box type thinktank bag that is not much bigger than what I carry a flash in. In fact I'm glad I've bought several eos-m bodies so I have plenty of backup to the backup. I never want to go to a smaller sensor size when this one is so perfect. What a great camera for teaching students of photography at the $350 price including raw shooting and processing. For the next generation, a swivel screen could be useful without adding much (if any) to the size factor. The eos-m with the 85mm 1.8 is quite a combination for candid's. I love this camera -- just not for my main camera.