The buttons soften before anything else does. Six washes in, they stop catching on jumper hems and start doing up in about four seconds flat, and that's the point you know the jeans have actually broken in rather than just broken.
Inside leg 34 inches, I need 35, so I've long since made peace with button fly jeans sitting half an inch short on me whatever the label claims, and I've stopped buying the next size up to compensate because the rise goes with it and then I'm hauling a waistband that sits under my ribs. What I will say is that the fly itself seems to protect the whole garment. There's no metal zip teeth to warp or stick after a hot wash, no tape to pull away from the fabric over time, so the front of the jeans tends to outlast everything else on them, long after a zip fly pair would have a gape or a jammed pull. Wash them inside out, cold, and don't tumble dry if you can help it, because the denim softens on its own terms and a dryer just speeds up the fading you didn't ask for. After a summer of being stuffed into a bag between a work bag and a change of shoes, mine came out with the usual crease lines across the thigh but no actual damage, which is more than I can say for a pair with a broken zip pull the same year. They pair best with something that doesn't need tucking in properly, because doing up five buttons under a jumper you've just pulled over your head is nobody's idea of a good morning: a loose shirt worn open, a long cardigan, anything that skims rather than something that needs careful arrangement at the waist. If you've never owned a pair, start with a straight leg in a mid wash rather than anything cropped or heavily distressed, because the plainer the cut, the longer before it looks dated, and a straight leg forgives the fact that the inside leg is never quite what I need.
Where they're the wrong choice is anywhere you need to move fast. Changing in a cubicle with someone waiting, dressing a child, anything against the clock, and the buttons turn from charming to genuinely irritating. I'd also think twice if you're pregnant or your weight shifts seasonally, because there's no give in a button fly the way there sometimes is in a zip with a bit of stretch panel, and once the waistband is tight across the top button it stays tight.
Worn under the same ribbed jumper I already own, they've made it look like I planned the outfit rather than grabbed what was clean.