I think the leather Apple cases are pretty nice, slim and surprisingly protective. Without a case, it's really slippery to me. It's easier to lose a secure grip on the 6/6 Plus than any of the past iPhones due to the size, material and rounded edges. To test this, hold it in your hand with the Lightning port facing the ground and very slightly loosen your grip. It will slip through your hand with just a tiny bit less pressure. I'm mindful to keep a tight grip mine tightly whenever it's not in a case. It hasn't gone flying, but I know it could easily slip without that tight grip. My leather case makes it require significantly less pressure for a good grip, so I don't have to worry about it.