PVS14 is a Night Vision unit.
FFP the RET. subtends correctly at all powers were SFP the RET. only subtends correctly at one set power. Most scopes are made in SFP. Over all I prefer FFP.
SFP scopes are good for:
Bench Rest / F-Class Shooting
Hunters in thick brush
FFP scope you can:
Rang at any power
Do holdover shot at any power
Hope this helps.
Mike @ CST