Hey man,
To answer your question the movable cover can be used after you install an aftermarket head unit. You will need to get some either a metra mounting harness kit or the one from crutchfield. Ive heard that the metra harness isnt that great and you have to do some extra cutting and drilling to get the after market head unti far enought back so that you can close the cover. However, i have heard nothing but good about the crutchfield harness, the fact that you dont have to do any extra modifications might justify the few extra bucks. Also if you order from crutchfield you get the wireharness and mounting harness for free and free shipping. I you use this code (PA166) you can get $20 off as well making it a great deal even if you price some units on ebay.