I put my JB in a clear Spigen case I had for my 6S to see and it looked like crap. The black shows every little speck of anything inside or on the case. A skin is the way to go for JB.
I dunno...a skin doesn't provide enough drop protection for me. And I've dropped my 6s probably about 15-20 times in the year I've had it.
But hey, if it works for you...that's all that matters.