I had one from WalMart on my VERY first AR, it didn’t hold zero and ended up in the trash. The reason you are not getting any responses is because not many people use these on AR’s anymore as an entry red dot optic. There are other more suitable optics out there at reasonable prices i.e. the SPOT from Grant.
Oh, and as far as covers go, Butler Creek has a large selection of covers, I had a set on my Tasco. I don’t remember the size though.