the phone's gorilla glass is strong enough to withstand most scratches. so, since the cover is just that (a cover), it's really not protecting much other than the glass when it is in your pocket. i don't carry anything else in my pocket other than the phone, so i don't run any chance of scratching the face.
opening and closing that cover, which is slippery, is scarier than leaving the phone naked as is. combine that with the fact that you have to open it like a book every time you want to access a function, and i don't think it is worth it.
Remember that the back of that cover is made the same way the original backplate is made.