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Both the Teammate and enemy show up similarly so it is a little difficult to recoganise the enemy and shoot but if you check the minimap and play a little carefully you can easily get the benefits.
BTW They also let you see through smoke, fog, mist etc.
They are quite useful in large maps or when all the noobs of your team are smoking the base and the best places to get kills.
But if you get used to TACs, it will be really difficult to play without them