The part where your foot rests is made of a very slippery material, so if you are in summer and your feet are sweaty these just keep slipping and slipping, and since they are not very well assured, the strap tears.
They broke the first day I wore them, also made me hurt my ankle and walk ridiculously on the streets in the middle of the day, with everybody watching me. Absolutely embarrassing. Threw them away the moment I got home.
Don't waste your money.