I had a Cx4 in .40
It comes in a zip - up style carry case that with a lock doubles as your storage.
I comes with a 2 point sling, cleaning kit ( actually really nice kit ) 2 mags and some pic rails.
There is a pull out rail under the barrel that is really cool.
As far as the mags having to be returned, I had mine and kept them, they were stamped 10 round mags. Im sure you can use the mags even if you get the longer barrel kit which makes it non restricted, somthing to do with them being pistol mags or somthing and the gov let them through. But dont quote me on this. Redleg or somone would know for sure.