I agree, every one has to got one on board. I have transferd fuel from spare to main tank on a 3 meter swell during a strom racing back to the harbor, didn't spill anything (and didn't het any water in the tank. It's much better than a funnel. It's also great to empty your tank for the winter.
It looks like a siphon tube with something stuck on the end, what is it (that end bit) & how does it start the siphoning action? do you have to pump it to start? I cant see how it automatically transfers the fuel, you must have to do something to get it going!
It's metal ball in a metal housing with two holes. If you shake it the right way the ball prevents fuel going back on the up motion and let's fuel through on the down motion. So when you've got the flow runnig you've only got te be shure the spare tank is above the main tank.