Have used the Du-Bro and Dots both. I use the Dots on my gassers since you can't flood a pumped carb and I don't need a third line. I like the fueler valves for my glow planes as they cut the fuel off from the carb when filling or draining, again removing the need for a third line in the tank. The only problems I've had or seen with the valves is sticking(mine always popped back out after a light tap) and I think I now have an older one that is sucking a little air past that outer O-ring, causing some leaning problems. Should be able to fix that with a new O-ring.
I did watch a guy one day trying to start his new Ultimate for about two hours before he noticed that the reason it was getting no fuel was that the valve had stuck.