Having custom models is all fine and dandy but they only work best in thirdperson (and we all know how Valve fucked it up with the aiming) due to (once again) Valve for screwing us over with the viewmodels.
Firstperson arms will still remain as stock survivors and unless you have a good thirdperson script (which many players don't even know about), your experience with custom models will be somewhat....lackluster at best