I have the cheaper Zaon version to which the good Dr refers. It works OK, certainly concentrates the mind when it tells you there's a target 1/4 mile away and 100' above. Trouble is it gives no direction information - but it does get one looking out of the window - which cannot be a bad thing. I don't like all of the wires it needs for audible warning in your headset (sexy female voice though.) Of course it does require the other aircraft to be fitted with a transponder that works and is switched on, which means it possibly detects about half of the aircraft where I fly.