Waste of money IMHO. The traffic could be just about anywhere.
Those that tell you the azimuth are a lot more expensive, and of not much use until transponders are made mandatory. Too many people fly around without transponders, or with them deliberately turned off.
I'd guess that TCAS would be more effective higher up, say 5000ft+, and certainly in CAS. But then you get a lot less traffic up there
I know someone who paid £25k for his system and he reckons it's great for IFR flying around Europe.