I normally rent aeroplanes with a Traffic info system in the USA and in the circuit it can be invaluable. Last time I was over we were in the circuit with about 4 other aeroplanes with a turboprop joining on the 45, parallel runway operations and aeroplanes coming in on an ILS for an intersecting runway. Scary place to be, even with traffic but at least we could see where everyone was despite the late afternoon sunshine and the mist, which made vis a nightmare.
I'm sure it did save our bacon once though. Same airport and we were departing straight out from a LH runway. ATC cleared a plane that had just departed from the RH runway for a "left departure". It was night time and we heard this and so were watching the lights, but of course it is difficult to see what is going on and where the other plane is going until it gets rather close. Suddenly we get a traffic alert, and so we stopped our climb and even started to decend and the other aeroplane went over the top of us at less than 100'. We were non too happy about this of course, but the controller was very apologetic claiming he thought the other aeroplane was higher.......
But for the grace of traffic-alert-systems.