I KEEP MY YAMUNAS IN THE SHOWER...
I have been using these Yamuna foot massagers for over 5 years now. I keep them in my shower tray and in that way I manage a foot massage on a daily basis. There as been a great response over time and note the soles of my feet are more supple.
I suspect they will have a preventative effect against Plantar Fasciitis amongst other benefits. There is an improvement in circulation and I suspect balance also. Just be very careful at the begining as soaps and shampoo etc can make them slippy. Always use an antislip mat where possible.