I have a Bushnell TRS-25 on my converted Saiga 7.62x39. It has been there for about a year (previously it was on one of my AR's for a year also). It holds zero and has no issues.
I have a Primary Arms RDS on a .22 upper, again no issues, but for the same money I would buy the TRS-25.
My favorite low budget but quality RDS is the Lucid HD7. It's very well built, has several different recticles and the optics are clear and bright. It was on my home defense AR until I picked up an Aimpoint PRO. The lucid is now seeing duty on my teenage sons AR. Search plouffedaddy's review of the Lucid.