I don't know about potato flour as egg replacer, but would agree with aitch about it not being necessary in burgers. Let us know if it does work though, as that sounds nice and simple. The commercial egg replacers work quite well, such as the imaginatively named "Egg Replacer", but there are others that we have used successfully when baking for example. And I know we have a recipe somewhere for a home-made egg replacing concoction that you can make out of ingredients you are likely to have in your cupboard. Will try to dig it out.