Apologies for jumping on this late Jim, I did ask about this for you last week.
The biggest advantage of the box is that it helps us see how the connection is performing against other suppliers. The data that Samknows collects help them provide a range of reports that are available to ourselves and Ofcom too.
Some of the measures include:
Average speeds both downstream and upstream
How peak periods affect average downstream rates
Latency & packet loss
Webpage load times
Video streaming time to start and buffering
From our side, we use the data to form metrics which help us understand how the service we provide actually performs from a customer perspective.
I believe Ofcom use the data in their reports too.
Hope this clarifies a bit.
ex-Plusnet staffer. Any posts after 28/07/2017 aren't on behalf of Plusnet