DFC
Nonsense.
"Mark 1 eyebal has kept me safe thus far "
It would do. The stats are such that you could fly blindfolded, outside and also inside CAS, non-radio, on random paths say between 500ft agl and FL100, and you would die of old age before hitting something. In the UK, you would see loads of planes appearing to be awfully close but the odds are massively stacked against contact.
It does happen but rarely, and when it does it is usually where people congregate (near airfields, on nice days preceeded by long periods of poor weather).
So, there is no statistically compelling argument for spending £15k-£25k (as some of my friends have done, in SEPs) on a TCAD-type system. Especially pointless with non-mandatory transponders; one sees well under half the traffic, with the % depending on how high one is.
But if for some reason you do want reliable traffic detection, you have to spend some real money (and make transponders mandatory).