60 Beats Per Minute feels a lot different than 100 BPM, which feels different than 140+ BPM. Once you get a feeling for how different BPM's feel to you if you have an abnormal elevation, like rapid heart rate at rest that would be an indication to manually check your pulse.

I'm just trying to say if you want to buy one that's cool but the premise that's it some kind of must-have life-saving accessory is questionable to me for the majority of people.