The magazine write ups and "road tests" I have seen on PCAS units appear to indicate that they are incredibly unreliable giving a multitude of spurious alerts ( usually from ones own transponder) . This would be a big issue for me for a system which would otherwise appear to be a cheap and cost effective solution to the problem, despite lack of accurate altitude or azimuth information
Just to go back to the point again about the fixation all the way through this thread about collisions in IMC, I repeat this is statistically by far the safest place to be if you want to avoid a GA collision outside CAS. There is in short, usually no bugger there. It is the low level VMC environment where the risk lies.