It comprises a steel ball on a short stem, with a clamp which clamps onto any flat tongue such as the slats on an air outlet. That bit is great.
There is then a tiny socket which you have to glue onto your phone. And that is the problem, as you then have to have that little 4mm-thick socket on your phone the whole time, making it difficult to slide it into a pouch or case. It does adhere really well, and can be removed pretty easily if you want it off, but you can't just put it on and take it off each time you use it.
In the end I mounted the socket on a clip-on phone case, which I then used as the mount, so that when I took the phone out of the case it was unencumbered by the socket. That worked quite well for me, but did mean that I had to carry a case for pocket use.
This device would have been much better for me if it had included a phone clamp which could be used for my phone instead of the stick-on socket. However if you don't mind your phone having a little socket glued to its back all the time it really does work well and is very neat. Thus it might be a fantastic mount for something always used in the car, like a SatNav or perhaps a speed camera detector, where you want to mount it on the dashboard and be able to remove it quickly.