Lee moulds are cheap = cheaply made and cheaply sold. Lyman and RCBS blocks, along with Rapine are of much superior quality and demand 4 times the cost, but you can still have issues with them, at times. Cherries are expensive and must be used for as many blocks as possible, sharpening as necessary until they cut a mould too far underize to be useable. This happens more often with bullet moulds, than round ball moulds.
My Lee RB moulds cast more balls that are out of round than do the iron or brass blocks of better quality moulds, but they are all useable for me. Yes- I know how to close the Lee mounds perfectly every time - they simply do not case round balls as often as my Lyman or RCBS moulds. In other worlds, the Lyman or RCBS moulds I have cast more perfectly round balls than the Lee moulds.
You get what you pay for. The .526" RB Lyman mould Taylor has, casts perfectly round .526" balls. I use these balls in the tight .530" bored pistol barrel of my flinter. They load easily with a .015" patch. My .395", .454", .495", .457", .451" and .684" iron moulds also cast perfectly round balls. None of my Lee moulds do as well. 2 out of 4 Tanner moulds cast perfectly round balls, while the other two are out about .002" which is negligeble and makes no difference.