The first figures are in.
8,117 people tested positive but only 5,407 provided details of people they had come into close contact with, about two thirds. There were 31,794 contacts identified by the system, but only 26,985 were able to be contacted and told to stay indoors. Of the 26,985 who were reached some 4,809 were incorrect, did not respond or refused to self-isolate leaving 22,176 who were prepared to play ball.
So basically the thing is only about 45% accurate. Yet given all that it shows that one person infected has the potential to pass it on to four others. Of course 'potential to' is not the same as 'is doing' but it is still quite a high ratio showing that we still need to take care.