The entire reason I have power meters (Stages left crank) on both my carbon bikes is this. My HR is super low and is NOT a good measure of how hard I might be working on a given ride. I didn't put one on my steel commuter as don't really care about power on my 8 mile ride to and from work. It is also the bike I use on my KICKR so no need for it there either as the KICKR handles the power.