I didn't see any significant difference in the Birkenstock. Very small and temporary change that definitely wasn't worth it

With the stone, I rubbed an old pair of Birkenstock-style slippers. The fur was rejuvenated but did not fully recover. I would recommend it if someone wants to extend the life of their summer slippers for another year. It should be combined with a cleaner and brush for better results. It would be good to lay down a cloth or newspaper while using it.