I wouldn't be surprised if those fans are simply rebadged 5 or 12V ones. Then again, for the price, hopefully not.

Pratically no, effficiency won't matter, the problem is KNOWING it's not perfect, for those of us who can't stand knowing something isn't just as we think it should be.

But really, for the price, I would be very surprised if they re-engineered the fans based on the difference of a couple of volts.