The biggest draw back to the swim heart rate monitors is they don’t provide live data while submerged in water; they need to store the data during the swim and then will transfer it after the swimmer exits the water.
Most of the data my GPS generates are things I need to see live. Heart rate is one of those things, but there is something else to consider: even if you could see that data live, how exactly do you view it while you swim?
In an open-water swim I’ll glance at my GPS during my catch maybe two or three times just to check out my pace. I wouldn’t have the time to check my heart rate, but it’s not one of those things I’m dying to know. I’ve been around long enough to be able to know what my body is telling me during a swim.
So, I don’t have the need for the swim heart rate data whether it’s live or post-race. Also, who wants to wear this each time they go to the pool? Odds are you’d need to wear a tri jersey to make it stay on your chest, at least for men. No one wants to wear out clothing if they don’t have to.