I have never used them. The only time I have seen them is in situations such as fast food places and catering trucks. Which tells me something about the food (although I ate the food, which tells you something about me). I have never done exactly what you are talking about doing, and I generally had an assistant with me, but, I preferred production hot service, that is to say, lay out 25 buns, top 25 buns, place top bun and wrap. Horrible alone, but, very fast with an assistant, no need to hold buns with meat.
me: I don't drink anymore
Yelonutz: me either, but, then again, I don't drink any less