Most of the cheap ones suffer from parallax errors, where moving your head moves the POI, but then you need to be paying Aimpoint or Eotech prices to not get those problems.

As long as you have a good cheek-weld it shouldn't be a problem.

Like you, I've just bought a cheapo "C-more" type sight for one of my rimfires, but as long as you're aware of the problem, it isn't one...