If I were to make such a vow my wife would assume one of the following. He's bought another one. He's just kidding and wants two more. He's off his meds again, not a good sign.
My wife and I have no joint banking accounts. We never have conflicts over money or how it is spent. Our bills are paid, our kids and dog are spoiled. So if she wants to buy something I don't care and the same goes for me. Best thing I ever did was to not open any joint accounts. I have seen countless friends end up divorced over money, who spends it and who earns it.
I never make the vow to not buy more guns. I know better.
My wife and I have a joint checking account and have for 43 years. I used plastic for almost every thing and she writes the checks for my Visa account. We both know how much money we have and are disciplined enough to not over spend.
