Stretchy straps ensure a good fit. The Hero sensor makes MUCH more sense being manufactured on the wireless mice lineup of logitech since it consumes less energy therefore it favors the mice time usage when using it wirelessly to save more battery. It is not water proof either. I have flat-feet, and the arch support is great. I made the decision to buy this one based solely on the aesthetic but wow! I wanted a bench for the mud room that was not particle board. Im questioning the long term durability of the case due to stretching to much so frequently. Really comfy, well worth £30 and also should last a few years as good build quality. They are good, but not good enough. I would not recommend them to anyone, and its incredibly sad because I adored how cute they were and the built-in ear LED effects.