This will probably not help much, but FWIW... a pilot who often comes up flying with me likes to take his portable transponder bug thingy (one wouldn't call it a CAS, would we?) As you pointed out, it gives you squawk, flight level, and distance.
IMVHO, anything that gives you extra situational awareness helps. What I can't make is a determination as to whether the cost matches the benefit, that is your call. All I can say is, yes, I find it useful to have those extra bits of info about other traffic in the area.
They're also nice to look at when you're #1 in front of a 737. Boy do they close in fast
