This handy little EMP doodad is badass. Not only does it take out all equipment but it also takes out sentries, guardians, dragon flies, AGR's and if thrown correctly will destroy the trophy system as well.
It disrupts all optics -being very useful for target finder and snipers- while also slightly disorienting the opposition though for a fraction of the time of concussion or flash grenades and is not countered by tactical mask.
A good way to destroy an AGR is to toss the EMP grenade and then either dive or go prone right by the AGR and shoot it. I don't think it can target you while you are prone right next to it. It might be able to run you over though I am not sure. As well it might not be able to target you because of the smoke and sparks of your shooting as the EMP grenade effects will in most cases have worn off by the time you are prone shooting it.
Feel free to add anything I missed about the EMP grenades usefulness.