Best alternative to heart math device ?

[captainamerica]

Can anyone tell me the best alternative to heartmath's heart rate variability training device (inner balance sensor or emwave 2)? 

I read that a couple top executives started using that in office to have control and mindfullness 10 hours a day. But it would look weird on me if I were to do it publicly :-D . 

So if possible I am looking for a chest strap with same type/level of training as heartmath's as that is very good.