I have a Samsung Gear 2 smart watch with HRM. Bought that mainly for the HRM for my bike exercises. And guess what. I paid another 400USD and bought a decent Garmin 510 bundle.
The Samsung HRM works good if you are sitting down and occasionally want to check your HR. However as it is not as good for any kind of sports none of the known programs(Strava, Runtastic etc.) are compatible with it either.
So my advise would be get a chest strap