Barn cats are like playing the lottery. Sometimes you win, most of the time you’re just throwing your money away. I have had 2 good barn cats in 30+ years. My most recent/current is Steve Buscemi (his eyes are messed up) he came neutered, tame and is an absolutely amazing mouser. If you’re a mouse or rat you probably refer to my property as the killing fields, just because of him.
The key is, once you get a good one, you need to get one little one every few years and have them protege, that way you always have a solid mouser on duty.
My two cents.