I've seen a lot of people here asking if you have SFL do you still need gunslinger, and vice versa.
Many people may know this, but in case you weren't sure, they do completely different things.
SFL increases ball velocity on set feet bullet passes. It does not speed up a QB's windup on deep passes or affect his release in any way whatsoever.
Gunslinger speeds up the QBs release on any/every throw. So if your QB has a long windup or a slow release (or both) gunslinger will speed that up. Making it very helpful if your opponent is bringing pressure. However, it does nothing at all to the ball velocity. It only affects throwing motion.
So, one affects how quickly.the QB gets the ball out and the other affects how fast the ball gets there once it leaves the QB's hand
If you already knew this , sorry to waste your time. If not, hope it helps