Back when I bought my Garmin (920xt) I bought a package with the HRM-RUN. I've been using that until a couple weeks ago. the plastic housing has started falling apart and my HR has become erratic with it. Mostly it's good, but when it goes wonky it messes up my metrics.
I've heard a lot of mixed reviews from the newer versions (red/blue strap) HRM's so I got on ebay and bought another HRM-RUN (apparently new).
My original HRM-RUN was on 6.60 firmware, the new one is on 6.30.
Getting this updated to 6.60 was a pain in the butt. I don't know if there's some way to do this, but my watch was not updating it, and my running dynamics were not correct (stride stuck at .63m for example).
I dug, around and located a source for the firmware for the HRM-RUN from here (http://gawisp.com/perry/forerunner/) (I downloaded the HRM-Run_660.gcd and HRM-Run_660.rgn files) I then followed this posts (http://suedkreislaeufer.de/?p=11154) suggestion and put both file into my garmin/remotesw folder and was able to update the new HRM-RUN to 6.60. I also renamed the files to match the post (6B175201.gcd and 6B175201.rgn).
I don't know if this will fix my running dynamics issue but I thought I would at least post how I updated my new OLD HRM-RUN to the latest firmware.
I *think* because my watch had already updated the firmware for the hrm-run (or maybe my previous watch did) this one didn't know it needed updating?? Just a guess. But I wanted to share my experience.
I haven't run with it since updating to 6.60 but it shows up/ connects to my watch fine. So I don't think i made things worse at this point.