I have been reducing my kit but still have a 5D2/50D and 750D. The smaller original M is essentially a 650D without the mirror box and the M5 an 80D without a mirror box.
I thought the M was a bargain when Argos was flogging them off at £199 but my M and M10 are pretty much first choice these days. I have already had a small go with the M5 and it feels great.
My DSLR kit is not getting used very much use, as, following a stroke in Jan 2015, my right hand is not great so grip and weight can be difficult sometimes. Weight is now a bigger issue.
If the M5 wins me over fully, then both the 5D2 and 50D will go. (The 750D will be kept for video though the M10 is quite capable too).
I started with the M as a walkabout but it slso takes EF and EF-S glass so it is capable of morphing to cover most needs. (Except the obvious like Motor racing, BIF etc, fine for cricket though [emoji56] .
The downside for me was the loss in tje M10 and M3 of the 'hotshoe'. I don't like the M10 pop up flash. At least eith the M I could use the YN622C TX controller with 622C units.to fire my speedlights.
Still thinking about that one !
The smaller kit bag, for me, is a big bonus.
Give the M a test drive. The proof of the pudding etc!