This item is not good and I regret the purchase. It was purchased for a gift, so it was not opened immediately after arrival and unfortunately the return window has now expired otherwise I would send it back.
The inescapable problem with it is the fit. There are other similar products that are well suited to typical human anatomy, but this one is just far too narrow between the two sets of moving parts and consequently is awkward, confusing and just plain painful to use, which totally defeats the point of it.
Our fit was fine, but it stopped working after 2 months. One of the screws had fallen out after a week of use, but we figured that out, after two months something shorted out and electricity stopped flowing through it.