So much this...
I *love* the flat sides.
I personally still use Bumper cases too. Bought a 20 pack in multiple colors off eBay from overseas and I swap them in/out and throw them out when they break down after a while, etc. At about $1ea, it's a no brainer and I love how minimal yet helpful bumper cases really are.
I used to use a thin case on my iPhone 5 (it is still working for me at the moment while I wait for the SE 2), but now I just use a sticker set for even more minimalism. I got one with chamfer protection. The strip around the outside covers the flat part and the chamfer. Just had to use a hairdryer to shrink it around the corners of the chamfer. Looks great (all in black) and is even smaller in my pocket.