The actual tracker unit is about 4cm long (a bit like a flat capsule) and it fits into a silicon strap. The top is a monochrome OLED display with a single capacitive button on it which allows various modes to be displayed. Underneath is the optical heart rate sensor. Once removed form the strap, it can be charged using the supplied USB charging cable which it pushes into.
There's an accompanying app (both iOS and Android) that sets the Band up (and upgrades the firmware if necessary). The app isn't the best in the world but it shows the number of steps etc. The band is also configured through the app i.e. what's displayed on the band and what notifications it gets. The app can also record activities (running).
The band will autodetect and track sleep, though there are two modes - one uses more battery life and is more accurate as it measures heart rate more often though the basic mode seems to work well too and battery life is very good, so far the band is on 82% charge after a week and a half of wearing so should get a month out of a charge.
Though not recommended for swimming it is IP67 splash resistant so can be used in the shower.
Considering the competition the price should be over £100, however it's available off Alibaba for around £16 including shipping to the UK.