I hate to say this because it's a primary reason I really liked the (idea of) the watch. I've had a HR strap for about 5 months and have really become a fan of having that information readily available while working out. I hate having to take all the extra time to put it on, get it connected yada yada. The watch, when it's locked in, generally seems aligned with what I expect based on learning my HR ranges from the strap. But there in lies the problem, the lockin is pretty crappy most of the time. I'll elaborate: I have the ML while I wait for an additional sport band. I've figured out through trial and error where the best spot on my arm for readings is and that's a few inches towards the elbow from where I normally wear it. I also make it tight enough (and the ML holds) so I'm not sure the sport band will help here. I think making it too tight actually interferes with the reading as well. The lock on takes too long is the first problem. If you are timing your workouts, then you want to start as soon as you hit go on the activity, which is when it starts trying to lock in. Quick changes in HR seems to confuse the watch, delaying the lock for 1-2 minutes in my experience. So since you start working out at the time it's trying to lock, you're pretty screwed to start. When I'm running, things seem to stabilize and it's locking in maybe 70% of the time. I think this is because my HR is pretty stable at that point. Elliptical though it seems to lock in maybe 15% of the time. I think the wide range of motion with the arms is interfering. I also wish I could see the HR on my phone in real time since I have a place on the machine where I can see the number all the time when using my strap. It's awkward to twist your wrist while holding the handle. Bicycling I have maybe 25% of the time locked in. I think this is some combination of vibrations and rapid HR changes as I climb and descend hills. I'm hoping this gets better with software and I know I can use my strap in conjunction but that doesn't change the fact that the activity HR is crappy in the real world for at least some types of workouts. I still intend to keep the watch for other reasons. ymmv.