I have one and I have used it for the last 8weeks and haven’t gained in length or girth, I was following the instructions that came with it and built up to 200reps a session.
I’ve never really had a manuel jelq routine but yesterday I did 200 manuel jelqs and I think I can get a better squeeze using my hands, I don’t see how it’s meant to be 10x more powerful than using your hand.
I squeezed the handles as tight as I could during a 200rep session and the only thing that happened was the foam came off and I ended up getting a cat like scratch by the metal rod.
I would say stick to using your hands and get a good routine going (something I’m looking in to).
If your still interested in trying out the device, try making your own:
Homemade Power JELQ