Backup Valve

Polaris, Letro, and RayVac all use a device to backup the units in order to clear it if it gets stuck. Someone had stated on the old forum that one of the three was far superior to the other two, and problems could be solved by changing the brand you use. I can't remember which was the best - can anyone help?

I have the Letro, it's almost 5 years old and still going strong. I don't know the differences between the three though.