I had an M18 for awhile and then an M21, they are both sweet lights (my wife EDC's an olight). David is in charge of all 3 companies (foursevens, eagletac and olight) so they all have some really similar, and really nice stuff.
Have you ever tied any DIY lights? I got into building C8 format lights last fall and have built several since Xmas. The new one I just order parts for should be the hottest yet. I'll be soldering these mcpcb directly to the brass pill on this one, should push around 1400Lm OTF, single mode with a 120second step-down timer that'll ramp down to 50% (I developed the driver programming myself). Again its not really an EDC, just a toy. For the $30 worth of parts its performance is unmatched in off the shelf lights.
I also have a securitying SRK in bound I'll be doing the resistance mods to bump it up to 10A on turbo, I have some samsung IMR 20R's I bought an interstate rebuilt tool battery pack just to harvest the 18650 cells from to supply enough current. It should be here in 10-14 days, the rest of the parts for this new C8 will take ~30 days.