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or do you have to have a case that protects the back?
I generally do. I have a piece of clear contact paper on the back of my Air 2. Simply for better grip and for scratch protection. Since it is clear, it is barely visible.

I prefer to go without a back cover because I can switch front covers depending upon my needs. Switching between a knock-off smart cover and keyboard cover.
 
just a smart cover, normally stays at home or if it is out and about, its normally handled by me so I know I wont drop it....
 
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