Believe whatever you want. Anyone who knows me well will tell you that I’ve done more studying of the science of running than most people out there. However, I also know when to separate science and lab results from real world experience. It’s nice to know why things work but it’s even more important to know what works. Based on a lot of research of what the best of the best do, including personally talking/running with some, there is no reason to believe HRM training works any better than running by feel and by pace.