I used to have a Garmin Vivosmart HR+ which worked pretty well but the battery started to die after 2 years. Heart rate tracking was hopeless for cycling - this tends to be a problem with wrist based HR monitors - but since I have an Edge on the bike this wasn't really an issue for me.
I'm sure the Apple watch is great for those with iPhones. If you're an Android user I can recommend the Samsung Galaxy Watch. Battery life is typically 3 days but I find that if I pop it on the charger while I have a shower I can push that out to 5 or 6 days. It's a very nice screen and a very solid steel body.