Personally I have never had a problem with X ball bronze
but all paint varies from batch to batch and how you personally have kept it. In general the less you pay the worse paint you get (not always the case but often)
Best bet, when your buying any ask to have a quick look at the bags for any 'square' balls, any broken ones or to check that they are all of a similar size with a good seem
if you can ask to do a drop test with it
-Mat