Toning shoes are that sector of the exercise shoe market that is designed to provide a tone up or additional exercise to the user. they do this by having an unstable design that make the muscles work harder.
There is not a lot of agreement that the toning shoes (more) actually achieve that. There is some legal actions and settlements with the companies that make the shoes due to the lack of evidence that they actually do what they claim that they do. Having said that, there are lots of testimonials supporting them. I guess this means that it is up to the individual to decide if these types of shoes are worth it or not.