The Wartenberg wheel is a medical device created by Robert Wartenberg to test neurological impulses and reactions. They aren't used that much anymore in the medical field but are amazing as a sexual device to add new sensations. It can be used by anyone and pretty much anywhere.
Varying the speed and pressure, the Wartenberg wheel can be used for mild to extreme sensation and is a good tool for those into BDSM, but this device does not have to used in a rough way. This particular one comes with a very nice pouch to store it in discreetly.