Bonus points for it looking like an actual watch too!
twas why I got the Polar M400.
it is both “normal watch size” and looks like a watch.
Needs Windows or OSX once to set it up. After that sync it once after a ride (or run, or swim, or zorbing, or one of a bazillion other activities) has finished via the phone app. Use browser to reconfigure* what you see on the watch for each sport type (and then sync via the app).
(* ie delete most things, and simplify what you want to see 😉 )
I think it does do stuff like phone notifications etc. but I cba with all that.
The only time you need to plug in the USB cable is to charge it (and flash new firmware, which I mainly do to make the nag screen go away from the app 😉 ).