Not relevant. I am surprised that you are trying to defend using EOS M to shoot wedding . Yes it can get some great to decent photos, but you will surely miss many. As Jim O pointed out the manual focus cameras of past had nice workarounds. EOS M is probably one of the worst camera I have used to capture the moment instantly (and its not only the AF, dead time between the shots has a good part to play too).
Regardless, this discussion seems to be pointless:
Can EOS M be used to shoot weddings: Yes
Can you get some great wedding photos: Yes
(Imagine a crazy scenario with 10 assistants carrying M toting nice L lens; randomly you would get some great keeper for every moment)
Are there better options than using M (provided same/similar glass): Almost everything else (except P&S and iphone)
Quite. If you have to relearn obsolete techniques to use a new camera, there's something wrong (especially when that new camera isn't designed for obsolete techniques either; that "dead time" you refer to is maddening).
The point is a fairly simple one, I would have thought. Everyone who buys an adapter so they can use the EF/EF-S lenses they already own probably owns a Canon DSLR; and that DSLR works better and is easier to use than an M and, unless it's an older model with a noticeably inferior sensor/processor combination, makes better images too. So unless, like Neuro, you simply want to use the M as an emergency back-up, buying an adapter seems far from being a "no-brainer" to me.