... but the problem remains PCAS only detects transponding aircraft. You may end up coming into conflict with a Luscombe (see AAIB Feb report) or Jodel without a power source for a Tx and PCAS - both power-hungry.
I tried the £300 one coming out of the PFA Rally some years ago. The sky was black with departing aircraft but not a squeak from the PCAS, which burned through the batteries in very short order.
When aircraft are outside CAS there is no requirement to be on radio or they might even have been talking to different operators. The Luscombe incident makes it clear that even if they had asked for a LARS service, it wasn't available.
Lookout isn't perfect by any manner of means, but often it's all we have.