The main problem I've found with inexpensive open back tuners is that the base plate doesn't hold the shaft with the worm gear very tightly. This causes slack as the worm gear loses contact with the tooth gear when first moving in one direction or another. And very often the hooks of the base plate are uneven, or the grooves in the shaft aren't machined smooth. This is usually the source of that grinding feel. I've tried to tighten some up by massaging the hooks on the base plate, but it doesn't work well.
My advice, which I think someone else mentioned, is to buy a set of Grover Sta-tites. Stewmac has them in nickel for about $13.50 a set plus shipping, and they're worth every penny. You can get them with bllack or white buttons. They also have gold colored sets, but they cost more.