I have sensitive skin and wore the sandal without socks for hours comfortably, no blisters or sore spots. The ergonomics of the vault was so back it took a nutcracker to open it. If I had looked harder I would have picked something that was easier to put on but these are simply amazing once you get your feet in them. I have rear feet but new balance and Solomon shoes have been my go-to for many years. I would do 4. But after two days of use so far - I would recommend. Disappointing - update a few weeks later they are now in bits. Function: 4In operation, the unit does almost everything quite well. Im retired and tend to hang around the house wearing house shoes a lot of the time. This is too deep for my kitchen units so we use it in the pull out larder.