It has turned into a shambles.
The original (correct) plan was to implement automated tracing done on Smart phones. That would have identified people who had been in close proximity to people confirmed as testing positive.
That would have meant tests were done on people most likely to have been infected, and increased the effectiveness of the tracing, and limiting further spread.
Manual tracing by cold calling and a questionnaire which would be very labour intensive, expensive and more hit and miss, was supposed to be a secondary measure - more of a mopping up exercise of those who slip through the net (by not owning a Smartphone for example).
But because the Phone app is a long time off being ready, the manual system has been brought to the forefront as the primary method of tracking, and will probably yield poor results.