I actually have, but is was low transmitter batteries that was the cause. There was a guage on the transmitter but the pilot wasn't paying attention to it.(maybe led lights would have drawn more attention)
The point is you can have the best ESV in the world but if you don't use it, it won't save your plane, same thing with voltwatch, but at least with voltwatch, mounted somewhere near the switch, you may notice a yellow or red light when you turn the plane on.