I have 2 arthritic knees and these sandals and shoes have been such a relief. I have been wearing them almost exclusively for the past few years and they have been the most comfortable shoes I have tried.  None have fallen apart nor have I had any trouble at all with the overall quality. I would highly recommend for anyone with troublesome knees to at least try them.  As I am not looking for the 'toning' aspect I cannot comment on that. The sandals do seem to run a little big. I am a true size 6 (measured by a professional); the shoes fit perfectly but the flip flops are a little long. The next size smaller was too small/short.