However, whether you need to buy your own special cobblestone mat is highly debatable. Looks to me like an attempt by researchers to make a few extra dollars to maintain their research funding (in the current research climate, unfortunate but perfectly understandable). Next we'll have long sandpits so you can experience the benefits of walking on the beach in the safety and comfort of your own home...
Some fringe researchers have claimed that strong sensory inputs from uncomfortable surfaces provoke stronger intrinsic muscular action and higher tone.
Robbins, SE conjectured that this phenomena was responsible for the arch raising/shortening and more lateral pressure distribution effects he saw with increased barefoot activity (the largest such effect was seen in those subjects who ran on rough terrain).
Maria Fusco from Italy teaches a theory based on selectively recruiting "hypotonic" intrinsics with rubber pellets inside insoles.
Her students use these pellets to treat postural asymetries and foot function.
Has this subject been investigated by more reliable sources?