what is the difference between building your own and this pump from amazon titled "Dyalis Male Vacuum Pump Sleeve Powerful Manual Vacuum Pumps for Men's Toys for Men Vacuum Pump Waterproof Easy-to-use Extender Enlargement Pro Extender"?
(https://images-na.ssl-images-amazon.com/images/I/61GvHuTddPL._SY355_.jpg)
One could build their own just be sure to have some sort of quick release mechanism for safety.