That's why I have said there is no value for money case here, and suggested simple ways to drastically reduce the risk of a mid-air.
Simply flying higher than the average pilot i.e. in the 3000ft+ bracket eliminates the vast majority of traffic, and those that do venture up there tend to be transponding and thus present a useful target to ATC radar.
There is very little chance of a widespread adoption of the £10k+ TCAS systems but a straight Radar Information Service (which is FREE) is all but worthless unless the traffic is Mode C or S.