OK, let's get this budget optic thread back on track...
OP, my buddy has a Sightmark and he has not had good luck with it so far. No matter how much he adjusts the quick release, it does not stay tight on the rifle. Tighten it down, shoot a magazine, tighten it down again. It also seems to be canted when mounted on his rifle.
To be fair though, his Sightmark was not new in box. It was a takeoff from a rifle sold to a pawnshop. Pawnshop owner didn't think that it added any value to the rifle, so he offered it to my friend for cheap.