I'm one that the Niles gave blisters to at WDW. I like them fine to wear around here, but at WDW all the walkig gave me blisters. I also have Crocs in the Beach, Cayman, Aspen, Athens flip flops, and and Disney styles. All of them are fine at WDW. It was only the Niles that cause me pain (alot of pain). They have a little ridge just below the big toes and gave me blisters just below both big toes and on the ball of my left foot. I thought it might be just that one pair, but I tried a different pair of Niles on another trip and they did the same thing. I round up in my Teva Mush flip flops both of those trips as they were all I could wear that didn't irritate my blisters.
I have now found Montrail Molokini flip flops and find I like them better than any shoes I've ever worn to WDW.