@Ian2:It's a nice device, battery life is okay unless you switch the GPS on and then it lasts about a day. Finding time to charge it when you are wearing it to monitor sleep can be a pain, but can I can get about 48 hours out of it on most days. I tend to put it on charge when I'm having a shower or washing up - because water isn't the Band's friend.
UV sensor is good, but not that I'm out in the sun much anyway.
Cortana integration is okay for simple questions, other wise the band will refer you to the phone.