They work on a points basis to a maximum of 100, the safer you drive the points you get which earns you a refund and discount upon re-newel. If you accelerate a bit harsh or like cornering quickly you get feedback telling you this, if you keep driving the same you could get your insurance revoked. Drive sensibly for 12 months or so, get a years no claims and you'll get the rewards longterm. It worked for my son and he really wasnt keen on a box but is now glad he got one. I do feel sorry for young drivers now, insurance companies just print their own money. My first car cost me £60 to insure Third party only, but then that was 26 years ago!!!
My first car was a Citroen AX, I paid 200 quid for it and £555 to insure. that was in 2000.
Now my wife and I pay £435 on an admiral multi car policy for a 2009 Mazda 6 2.2 diesel and a 2012 Seat Ibiza diesel.
It's all about risk, young (especially male) drivers are a high risk therefore should pay more to insure their cars. These black boxes give them the opportunity to show how carefully they can drive and get rewarded for good driving