I just got these, wore them all night, woke up, no pain in my back.  I'm always in pain after wearing flip flops.  These are great, HOWEVER, The strap is a bit tight.  I do wish it would have been 1/2 size larger, or longer in length.  If you have a NARROW width foot, then true to size, NORMAL TO A BIT WIDER, GO 1 FULL SIZE UP is my suggestion.
Turquoise color is really pretty!