45RackerTracker
It's not usually recoil that people care about (though some with shooter's elbow do), it's getting back down on target faster. "Felt recoil" is one of the indicators you can use that something is helping because it can mean your hand is not being knocked out of position as hard. It can also fool you, though. Actually timing your runs and checking your accuracy on follow-up shots is the only way to really tell.
In the case of the squared firing pin stop, you trade ease of slide racking off against reduced muzzle flip. After installing it, a friend observing me shooting from the adjacent firing point said my muzzle flip was visibly reduced using it. It is a drawback if you have to rack the gun during a clearing drill (a bit harder to start the slide rearward), though I don't find it a great drawback. The other thing it does is delay the start of the slide into counterbattery, and if you have a barrel with an unsupported chamber breech, this added delay can reduce case bulging.
Nick