Nothing wrong with an AEP. As a backup weapon for when your primary runs out of ammo/battery, anything is better than nothing. I even ran with a springer pistol for a while.
I must admit though, I had a AEP Mac10 for a couple of games, and found it to just be not up to scratch compared to the alternatives. The batteries couldn't be charged by standard smart chargers, and they didn't stay charged for particularly long. The gun itself felt weak and had terrible range. It felt like it was going to fall to bits when on full-auto. I sold it and bought a not-too-fancy GBB pistol, and have never looked back. For what is essentially the same role, I personally think that gas pistols are superior in most ways.
(as to answer the first question, I use mine lots. Running a DMR, but still liking to be at the front of the team, it comes very much in handy for pushing in close on objectives and for when the other team push back. With a sub-350FPS AEG, it's useful for stoppages and when you don't have enough cover to maneuver a full length gun around)