If you take your training seriously enough that you are interested in tracking your HRV, I strongly recommend you just get the Bioforce system. I used the cheaper HRV systems and they just don't work as well. Plus if you go with Bioforce you get Joel's book and access to his online tracking system. While the book isn't very long, it's very valuable to understanding the HRV numbers, which is much more complicated than you probably think.That being said, if you just train recreationally, I think the HRV system is a waste of money.
+1I bought the Bioforce purely because I wanted to play with it and I was curious.Long story short, if you're on a team, or being coached and lifting seriously, I can see it's value, especially to the coach. But I found little to no value in it, and it sits in the closet, unused for me.