I've got quite slim wrist but am used to big watches. The charging works well as long as air temp is below 90 Fahrenheit at that point it can't charge.
The strap is uncomfortable and it looks a bit toy like in the flesh, had I viewed in a shop it would not of been bought.
Step counter seems to work ok, the run function seems to need to be told when to start and stop, but I don't run so not used it, backlight is only from 4 o'clock on the face and doesn't light it up very well.
Sleep function I have no idea on as I'm sending it back and didn't want to damage it during the night.
Thinking about the new galaxy watch instead as I can see it in a bricks and mortar shop, and will stick to my eco drive until then.