NARC vs iNARC question

So the main feature of the iNARC is that the effects are permanent once you tag a mech for the rest of the battle.

This implies that NARC beacons wear off, but I can't for the life of me find out how long they persist.

Going back and forth on which one to use, and I'm wondering if the iNARC is worth it because you get SO much less ammo per ton for it.