The newer devices certainly offer TIS like performance and FLARM, the latest one I have seen is
LX avionics Ltd - Traffic Monitor which with the capability of adding mode C looks a very capable unit.
I'd love to think that I can spot all the other traffic - but I know I cann't. In this neck of the woods high speed military traffic can be found pretty much anywhere in the usual VFR range of heights. Spotting a single aircraft is really bad news as they generally operate in pairs - so any odd number suggested you have either missed the leader or the wingman - which? you'll never know......
Gadgets like this would really help.