I have just started using a Trafficscope VRX, although it doesn't provide azimuth information it does mean that your aware of traffic that you haven't seen. It will never replace a very good lookout but does serve to show how many acft are out there that you miss, it's increased my lookout and paranoia
If it has any benefit it's that you will re prioritise your work load to locate
a threat that you haven't seen. The audio warning means that you don't spend any time looking at the VRX.
As IO540 said a surprising number of aircraft don't use/'turn on' a transponder
which you will get no warning of.
NTB