There seems to be a lot of choice, so advice please.
I also have the Flex and can't see any need for anything more intense than this, and if you do then I recommend just going full smart watch. It's a decent bit of kit and the app is fantastic, it's really interesting. I got one before it was cool here because my american mrs got me one over there and it's absolutely mental there, everyone has one. I reckon you should get the flex, just because I feel the heart rate stuff is just a gimmick.
Is the HR the same as the Charge?
There is the 'Charge' and the 'Charge HR'.
The Charge HR being the next model up (HR standing for Heart Rate, in case that wasn't picked up!).
Edit: Charge = £70.00
Charge HR = £100.00
Ah okay understood. For the extra £30 it seems worthwhile to get the heart monitor as well then.