The initial first pull is long (not quite as long as the FNX's), but it's lighter than the first pull of the FNX. The FNS also has a short reset, meaning that you don't have the long pull for subsequent shots if you don't let the trigger all the way back again, so the follow up shots have a short trigger similar to the FNX in SA, but heavier than the FNX's SA (as long as you just go to the reset point and pull the trigger again - which is pretty simple and allows for fast follow up shots).
Hopefully that's clear. It makes sense to me, but then again, I wrote it :?: