I've been using the faux CF battery cover for a while now and I think it's a great change. I gave the metal and chrome battery covers a try and they killed my phone's signal reception.
I permanently attached my wireless charging pad and NFC antenna to the back, and the thickness increase is only slightly detectable.
No loss of signal. The feeling is slightly grippy and rubbery but not "cheap". I think it's way better feeling in the hand than the OEM cover and looks MUCH better. I don't handle my phones like a family heirloom and this is standing up to my mild abuse just fine.
Without a doubt, for 8 bucks, I recommend this if you're looking for a different cover for your S4.
Amazon.com: Black Carbon Fiber Plastic Material Replacement Battery Cover for Samsung Galaxy S Iv / I9500: Cell Phones & Accessories