me, my brother, and my father in law are all running the cheap 30mm truglo red dot (2 AR's and an sks) without problems. I can't say we've ever had a problem with the dot wandering or shorting out. it's not perfectly clear, the dot's not perfectly round, etc, but they've worked. the scope caps that come with it are garbage. the cheap tasco red dot on the 10/22 has wandered some.
also, if you get a dot with the built in rings, you'll need a riser. I had a flat top with no front sight and tried to mount low, but it was too low. if I was buying today though, I'd get the millet red dot at academy for $60.