A lot of what happens to the rockers has nothing to do with the rockers themselves. While I'm not a fan of cheaper stuff (or perhaps a better way to present that is I understand what getting a cheaper product to market entails), my impression is you had other issues causing you problems. For instance - a bad valve job, incorrect valve springs, or valve spring setup, bad guides, overtightening attachment bolts, bad or poorly installed cam bearings, bad or incorrect pushrods, bad lifters, or over-revving can all cause damage to rockers that otherwise would be fine.