It's an Ares CQB M-4 S-class. You can also get them in tan. I paid $200 for mine and it came with the battery.
It also comes with this comfy forward hand grip.
I bought a $50 reflex sight for my CQB field. It has four different dots, two different colours and three different light settings.
I bought eight mags for $40. They have a few feeding issues and are pretty heavy since they're made of metal but I couldn't pass up a deal.
Field stripping is pretty easy. You just take out two pins and the upper receiver slides off. I may get into customizing the internals and all that but for right now I'm just happy to play.