Durability isn't the issue. Any decent quality BB should effectively last forever. By which I mean the spindle and cups; replace the balls and rollers as needed. The neoprene seals are full contact, which significantly improves cleanliness, at some sacrifice to friction. My issues are 1) the tiny, and loose, ball and needle bearings that fall out of their "retainers" causing no end of grief, 2) the difficulty of adjusting the assembly to a correct preload after cleaning and re-installing (a direct result of those little ball bearings), and 3) the lack of good working diagrams showing the separate sleeve, and correct position and alignment of each part. Doesn't take much to fix all that.