Gaseous,
I have flown a few helicopters with TCAS fitted. IMHO they certainly help but they are not the complete answer. I have had close encounters with TCAS: sometimes other aircraft do not appear to have their transponders on in the open FIR. Also fast jets move so quickly, you do not get a lot of time. It is not a substitute for Mk1 Eyeball.
For a Robbo, TCAS would be a very expensive add-on at around 50% of the cost a secondhand R22. If you were talking about the new cheaper versions, then I don't have any direct knowledge about their use. Unlikely to be better than TCAS though.