The Karas Kustoms case for the iPhone 4 is a CNC machines aluminum case with a very industrial look and feel. It's not everyday you see someone using an iPhone with this kind of case that's for sure, it might even give you some street cred. This case has two parts two it and uses four screws on both sides to secure the case on the iPhone 4 using a small hex key. Karas Kustoms includes two extra screws in case you lose a few as well as the hex key. The Karas aluminum case isn't really a case but more of a frame for your iPhone 4, it coveres the front and back edges all around while leaving the metal band of the iPhone 4 completely opened.
Because of the openings all around the iPhone 4, you have very easy access to all your buttons and ports as if you don't have a case on at all. The Karas case does recess the iPhone 4 all around so that your iPhone's metal band is protected and there are no signal issues too. The Karas case is very lightweight being fully made out of aluminum but it does cause a big concern as there is no padding or inner lining what so ever. It's a big problem because there is direct contact with the metal and the iPhone 4's front and back glass, and upon pressure like a drop it could possibly cause damage. There is absolutely no form of shock and impact absorbent on the Karas case and it's something that I think hurts this case's potential. Even the black corners that house the screws are made from hard plastic instead of some kind of rubber.
Other than the fact that the Karas isn't the ideal option of a protective case for the iPhone 4, there could be some discomfort while holding the Karas in your hand because of how industrial it is. There is however a good amount of "purchase" grip because how the way it frames the iPhone 4 and creates these places where your fingers can get a hold of. There are no sharp corners and the overall build quality is pretty great.
I have a Phantom Skinz matte back protection on my iPhone 4 that I would recommend having on if you're using cases that have opened back parts like the Karas and others. If you don't over tight the screws on the Karas (which you shouldn't!), it will not bubble or lift up any of your film protectors that you might have on. As you can see from the images there is a nice lip on both sides which gives a nice lay-on-the-table design. Karas Kustoms have a few different colors available including a few limited edition metals other than aluminum like brass and copper.
So overall I think the Karas Kustoms aluminum case for the iPhone 4 is more of a show-case than a protective case as of now. It definitely has that cool factor that you might wan't to just have around when you go out but not it isn't an everyday use case. Price $39.