[samatman]

I don't see any compelling reason to choose this over the Anker battery either, but some people don't even consider off-brand accessories and Apple is happy to charge them double or triple for the privilege.

I think 5W is a deliberate design choice, though, for exactly the reason you mention: heat. You can slap the battery on and stick it back in your jeans without roasting your thigh, and the point is to keep your phone working, not to make the battery meter go back to green ASAP.