Button fly jeans are a shit. For the first few weeks, they are impossible to get done up (this flies [flies? geddit fnarr fnarr] in the face of the unspoken in-and-out-as-quick-as-you-can men’s room rule. Nothing worse than finishing at the same time as another bloke, and while he’s finishing up washing his hands, you’re still there making strange jiggly hand movements down below).
Anyway, the buttons start off as impossibly tight to do up, and then somewhere in the life of the jeans they go straight to being loose, and you’re walking around with your fly open all day. There is no period where they work as intended.
Give me a zip any day. This is the 21st Century. I’ve had trouble with zips, but very, very seldom. Most of them are still working properly when the jeans fall apart. But every pair of buttom fly jeans I’ve owned has been a hassle.