I had a Star BM (Spanish 1911 clone). It had the bad habit to go from condition 1 to condition 0 when carried in a holster. It had go.
My Uberti 1873 rifle developed problems and had regular FTEs. The waranty repairs failed to correct that. It was replaced by a Winchester 1873 rifle. The Winchester served well for several hundred rounds so far
.
A Glock field knife proved to be not up to par. Due to the short tang it lost the blade when hacking off a branch and I was not able to retrieve it. Luckily noone was in the path of the blade.
A cheap charger ruined a set of rechargeables when a capacitor blew. I should have bought a better one.
Finally not really a regret but a tool that was drastically reduced in usefulness is a Leatherman wave. I canīt carry it legally anymore as the blade can be opened and locked one handed
.