I think it's an excellent tool, and should be in every cockpit. Since we got them, I see probably 5 times the traffic I did before. After seeing a target on the scope, we start concentrating on a specific area, and often see traffic we would never have seen otherwise. It is certainly not infallible, and is just another tool, mostly for use where there is no ATC. I would never assume that there is no traffic just because there is none on the scope, but I'll take all the information I can get.