Nippon

Hi Guys. Out of curiosity, what's the caveat of getting a non-oem axle? From what I understand, most (if not all) aftermarket axles are solid as opposed to hollow. I can understand the obvious weight savings but what else do I stand to lose from opting to get an aftermarket axle? Also, I've read that NAPA axles are very good replacements for O.E. Is that true?