I would buy both because I love tools - so any excuse!
If I was trying to justify the expenditure to my wife, I would explain that I would get a new gear hanger and fit it to the bike and keep the bent one as a spare once I had realigned it using the hanger tool. A damaged hanger that is a few mm out of alignment is enough to make it impossible to index the gears correctly - so if I have trouble indexing gears I always check alignment and have found it to be the cause of the problem on a few occasions (I service bikes for lots of people) The tool has always enabled me to sort the problem. When I still rode an upwrong, I had a Claud Butler Dalesman which had suffered from a rear derailleur failure and the mech had got thrown into the wheel causing the rear dropout and hanger to bend as it did not have a separate aluminium replaceable hanger. The bike would have been useless if I had not been able to realign the hanger.