Gotta agree with all of that.
If I had no lenses to consider, and wasn't sort of latched into the Canon system, I would probably look very closely at the Sonys.
But since I am sort of married to the Canon system, I got an EOS-M a few years ago because the "kit" was amazingly cheap. I think I paid $220 for the body with the 17-55mm lens, and have been getting a huge amount of use out of it ever since.
Let me rewind back a ways:
I have a lot of Canon gear from the early 1970s and on through about 1978, FL and FD lenses, FTb body and a couple of F1s, motor drive, etc. I worked at a newspaper for a few years before getting into electronics, and this gear served me well.
I never suckered into that whole autofocus business, so that's kind of where that stopped.
Then about 1998 I got my first digital camera. A Kodak. That lead to more and more digitals as they got smaller, better, cheaper...
But they always lacked the manual control and, of course, TTL viewing. So I finally got a 20D, and then started building a lens collection to work with that. I Got a 40D at one point, and have used those bodies ever since.
The manual FL and FD lenses and those bodies sat unused.
One day, I was at the shooting range, and a tornado hit between the range and town. All of us stopped shooting, wandered over to the edge of the 300 yard range, and watched it. It was spectacular. All I had with me was my Cell phone that day. I'd had a full DSLR setup with me the day before, but alas. So I got some really excellent 640X480 shots of that tornado. When I showed them to people they could see the tornado. Except it was actually a light pole in the foreground.
After that, I resolved to NEVER be without a decent camera. So I got a little Sony which actually is quite fantastic. Zoom range equivalent to 24mm to about 200mm. Shoots full HD video. Extremely compact. Wonderful. It went with me everywhere, and I got a lot of excellent use of it.
But when the EOS-F came out, and was selling for so cheap, I got one because I really did miss having RAW format, the larger sensor, and interchangeable lenses. Plus, because it's so thin, you can use a simple adapter to let you mount all of those old FL and FD lenses! So I could blow the dust off of them and finally get some use out of those.
And with another simple adapter, it'll mount all of the EF and EF-S lenses. So it's compatible with every single Canon lens I've ever bought!
Not that it's really the body of choice with a huge lens mounted to it, but it works. And it shoots video, which my 40 D doesn't do, so it filled my desire to play with that, yet use my existing "big" lenses, too. Macro video with the MP-E65! Wooo Hoo!
Anyhow, my situation may be like yours in some ways.
While I really wish Canon would jump into the mirrorless world with both feet and get serious about it by building an EVIL (electronic viewfinder interchangeable lens) body to use the "M" lenses, the existing M and now the M3 or even M10 (a more budget-minded M body) are there for us people sticking with Canon.
I have yet to get an M3, but I may. My brother got one along with the separate (but apparently quite excellent) electronic viewfinder (it mounts to the hot shoe). He says the EVF is great.
I miss an eye level viewfinder at times. And I'd really like to see Canon offer an "M-like" body with the EVF built in. But I have gotten excellent use out of the old "M". The low-light performance is light years ahead of my 40D, that's for sure. And the IS in the kit lens is great. I've gotten more amazing existing light shots since getting the "M" than I would have imagined.
Now that we've got grandkids, I tend to take it everywhere, and it's allowed me to get what I consider to be very acceptable kid shots in amazingly dim light.
I have used it with my old FD 55mm f/1.2 lens, and with it's 1.6X (APS-C) sensor, that lets me pretend I have an 85mm f/1.2.
However, I do notice that the old lenses are not anywhere near as great as I remembered them. Film hid a lot of imperfections, actually! Still, it's nice to have them available again.
The video is handy. The "M" lenses are good. And despite early reviews, the updated firmware makes the autofocus quite usable. I'm sure the new M3 and M10s are a LOT better, but I've not found the old M lacking much, actually.
So in conclusion, I think Sony has taken this idea and run with it better than Canon has at this point. But if you're kind of stuck on Canon the way a lot of us are, I do think the M3 would be a good way to dip your toe into the world of mirrorless.
I use the big, huge DSLR gear when I want a true optical eye level finder. But that's less and less often. The smaller kit is something I can haul around and have with me so much easier.
And really, there are some excellent cameras out there now that do not have interchangeable lenses. For the ultimate in compactness, some of those really are getting to be a viable alternative to a DSLR and bag-O-lenses, too.
Nothing that I've tried yet matches the feel and absolute speed and utility of a full-sized DSLR. But portability really is a consideration. You never know when you'll see a tornado, or bigfoot, or a UFO, or maybe a grandkid doing something adorable!