I got one of these for Christmas last year and it's disappointing to say the least.
First of all, when you push the device down on your head, the prongs tend to bend in the wrong direction so you have to rearrange them with your other hand otherwise you end up with most of the prongs on one side of your head. Also, you only feel the prongs on the widest part of your head where the most resistance is.
It is nowhere near 'strong' enough to be deemed a massage either. At best it produces a very light scratching feeling. I like the feeling of my head being slowly scratched. This feels like that but on a very light note so not enough to be really satisfying.
I don't believe anyone that says 'oh this is a lovely massage after a hard day at work' because I get far better results from massaging my own head. Plus that way I don't look like a fool with my arm above my head pushing a pronged object down on my scalp. I don't get an arm ache either.
It doesn't massage and the prongs bend out of shape easily. If you want to waste 5 pounds on a very very light and subtle head scratch that you can only feel on a tiny part of the side of your head then go ahead!