i confirm its usefulness for a flat footer like me. after i wear birkenstock and change shoes to more support type for running shoes, my knee and lower back no more pain. Last time wear crocs will feel pain especially after standing for quite long.

Cos last time i owes got lower back pain, but go doctor do mri xray no slip disc, doctor say maybe becos muscle strain due to flat foot, ask me change to flat foot footwear.