Toning shoes like the MBT’s, Skechers Shape Ups and the Reebok Easy Tone were very popular as exercise shoe to get that extra tone up. That was until the lack of evidence supporting the actual tone up from the shoes and the legal settlements been some companies that made these shoe and the Federal Trade Commission occurred. The shoes are designed to be unstable, so they make the muscles work harder due to the imbalances created. The companies made all sort of exaggerated claims as to the benefits of that extra muscle activity. As the evidence did not support the claims, the FTC pounced and held them accountable. The moral of the story is that if you make health or medical claims for a product, then you has better have evidence to back up those claims.
However, the toning shoes still do have some good uses. They are helpful to make the muscles work differently for a short period of time. This may have some benefits for athletes. They also make be very useful for hallux rigidus. Some clinicians also like to try them for those with chronic postural problems, as they do make a change to the gait.