The cheaper the mount, the less reliably it will remain attached. The super-cheap ones often don't fit the carry handle channel well, and will have a super-cheap screw that holds them on. The better mounts have a nut that is designed not to come loose with recoil, uses a screw that fits the screw hole in the carry handle perfectly, and will fit snugly in the carry handle.
Having said all that, mounting optics on top of the carry handle is the worst possible setup. Getting a good cheek weld is impossible, and the sight is so far above the bore that there is a radical change of bullet impact (compared to your zero) even with only minor changes in distance.
What I'm getting at is that you'd probably find it much better in the long run to change out to a flattop upper if you're going to use anything but a forward-mounted dot/reflex sight on your carryhandle.
-Troy