U/U?
unique? and u...?
Unique/untradeable

Untradeable.

I don't agree with OP, however. Maybe if it charged into doing a special ability or you'd be able to activate that bonus for an hour or two it'd make sense, but charging SB isn't hard at all if you'd have to do it once.
They could make the charge time for SB slower for U/U gear, The reason why i suggested this is because some people want materia to U/U but i Materia should stay crafter only. Doing it this would make some U/U gear more sought out, the stat increase does not have to be as extreme as i said.