I like the PEV. I have used it at several contests now (Polish Nationals and PanAm). There are several variations on how the PEV can be used. One is to push the button x minutes before start, the other is to push the button before crossing the start line and you can't restart for x minutes.

I prefer the later, push the button just before starting. This can work well for getting rid of leeches. You can fake a start and then come back and the leeches are stuck with the earlier start. This technique also works well when you are working a thermal that is on or near the start line. You don't have to worry about accidentally crossing the line until you are ready..

The other techniques of pushing x minutes before has the issue of needing to make a window of x before, but you must start within a certain period of time. Without the window you can just push the button off tow and start at any time later. You also have to careful to not cross the line until you are sure you are ready to go, otherwise you have to wait for the interval again.