They have the same internal circuitry, and the tested (vs. written on the battery, which is often BS) mAh of both is effectively the same. They both have the same "Off" approach, slightly unscrew the bottom cap and it breaks the connection. Both of them work with the TR-001 charger.
It pretty much depends on which form factor you prefer, longer and skinnier vs. shorter and wider, though it isn't also that huge a difference. The Buzz Pro might have a slightly larger drip well than the IPro, though I just use carto tanks so that is a don't-care for me.
I have the original Infinity, picked up a Buzz Pro when they came out, like both a lot. As I posted elsewhere, I run 6 - 7 ml of eliquid, at about 8 watts, between battery swaps, using 2.5 - 3 ohm cartos in the 4.5 - 5V region. To me that translates to full day.