I have the most advanced jelq device from jelqgym. And i still prefer to use my hands. Frankly speaking i dont think it is that easy to make a device which will work better than hands.
Basically you are being sold a canning tool. You can grab one at Walmart for about $5. I prefer my hands and teh [words=https://officialhydromaxpump.com/?uid=6&oid=2&affid=98 ]Bathmate[/words] personally.