I’ve got a Polar M400 and it’s a fantastic bit of kit. It has way more features than I’ll ever need. The activity tracking stuff is good too, if you’re also looking for something like a Fitbit but with proper GPS and HRM support.
But jeez, Polar’s software is just awful. They’re about the only GPS manufacturer who don’t support automatic uploads to services like Strava etc. Their own web service is pretty awful and mostly exists so you can go online and export it for uploading to other websites. The Android app is pretty bad too.
Shame really as the hardware is great and their customer support is brilliant – I’ve had mine fixed under warranty twice now. They’re easy to deal with and my watch was returned to me the next day (sent special delivery, fixed that afternoon, came with the post following day). I’d recommend them as an alternative to Garmin if you aren’t fussed about having to manually export stuff to add to Strava.