I am deep into the Polar community. Their HRM is the gold standard with published/peer reviewed studies backing their claims. They have watches that can be love/hate compared to Garmin and other brands depending on how serious an athlete you are.

Polar has an app, Flow, which allows you to use their HRM (and other brands) without a watch. You can log all your workouts and it’ll show you all the stats and graphs you’d ever want. Polar can give you running programs and other workouts and you can write notes in the workout to record anything custom.