I'm interested in this topic as well. I've had a heartmath inner balance for about a year and have been on again/off again with it since I bought it.
How do people achieve the super high scores I've read about? I've seen people average over 7 for a session and that seems impossible to me. Has it had any positive effects on your stress or sleep, if either were ever a problem?
What is the recipe for high coherence?
Guys from https://studymoose.com/ done an essay on the topic for me and in most cases I don't even get into such topics but this time I got quite interesting so I'll be tracking the thread for further replies.