Arcade works.. wtf!

Theres a little more to it than that. It adds a brand new connector that sits higher up and expects the cart to go in straight on. Then the spring loaded tray is replaced be a solid piece of plastic that sits perfectly in the front loading opening and guides the cart straight in. This allows not only a better connection than using a game genie, but also allows you to close the front door while the system is in use.

 

looks easy to clone, without the need to actually buy one to copy.
2 edge connector sockets and a simple single sided PCB. The only hard part would be the tray but would it be cheaper to sell little clips to make the stock tray stay in the upright position...

 

If you could do that, you already have my money.