1: This isn't designed for m-lok or key-mod, it's actually designed for 'standard' type handguards. As in the 'round-plastic' style ones that usually come on 'budget' minded AR-15s. You might be able to fiddle/modify this a bit to work with mlok/keymod, but I would just buy something intended for those systems... This works great for what it's made for, I have it on one of my ARs and am actually waiting for another one to ship from optics-planet so I can put it on that one as well...
2: The width is about 1" it goes well with the standard handguard, doesn't look weird or anything.
Now I used a little blue loctite on the threads of mine and snugged it down pretty good, no wobble or flop from it. I did end up cutting mine down though, shortened it up a bit so its more of a stubby hand-stop and it works good. I never bothered with using the storage feature anyway, but to each their own...