This app was mentioned in 3 comments, with an average of 1.67 upvotes
It blows my mind that there is still not a device that matches the features of the Microsoft Band that was released 2 years ago!
Custom workouts, on board GPS, workable text input... Turns out these were ahead of their time.
The closest solutions I've found for the custom workouts are an android wear device running the Atlas app or the latest Garmin Vivoactive 3...or just keep replacing the band 2 from ebay.
Any Android Wear watch can continuously monitor HR. The reason most don't by default is because these optical heart rate monitors draw a relatively large amount of power (due to the LEDs, extra processing, etc) for the small watch battery. As an alternative, some apps will kick on the HR sensor every 5 to 15 minutes to give a "continuous" experience, and in most cases this is sufficient for all-day monitoring and a good balance between all-day monitoring and not killing your battery.
If you're interested in continuous monitoring for fitness, (disclaimer, I work for Atlas Wearables who developed a fitness app for Android Wear), there are apps out there that will continuously monitor HR for the duration of your workout, like the Atlas Wear app: https://play.google.com/store/apps/details?id=com.atlaswearables.ionic.androidwear.lite
The Atlas App (i do work for them) will show your HR, estimated distance/pace and active time. It also is able to pick up on bodyweight exercises like pushups and crunches. https://play.google.com/store/apps/details?id=com.atlaswearables.ionic.androidwear.lite