This is my second iteration of the HRM-TRI strap, same product basically. I used my first for a year and a half, including through a full Ironman training cycle, before it went kaput. It required changing the battery once, maybe twice. I was hoping it just needed a battery, but no dice. I guess I did get good use out of it. Wish it had lasted longer, of course.
This product is getting a little bit harder to find. When I called the local running/triathlon store, they claimed that Garmin was "phasing it out" in favor of the wrist-based HRM. I think/hope they are wrong. The wrist based HRM system is good and improving, but it has several flaws. It is well established as less accurate than a strap. VO2 max estimates, for example, when compared to true lab measurements, are off by 1-2 mL/min/kG, whereas the wrist-based measurements are off by 5-10. This strap produces more running dynamics (not that I care about most of them), and can be used in water (though of course, still no real-time HR data). I think it will be some time before wrist-based HR is the gold standard,.
This strap fits better and is more durable (despite me living in it for many more hours) than the HRM-SWIM, which you can buy in a bundle with the HRM-TRI. (If you swim with the HRM-TRI, you really should be in a tri suit or wetsuit to keep it in place.)
I have bought numerous Garmin HRMs in the past. The TRI I think is quite reliable compared to earlier versions, many of which had issues with "spiking" or "dropping" your heart rate feed. This can be disturbing when it happens. ("I just started running! Why is my heart rate 200? Is that even possible??") The workaround is to use a Polar strap with the Garmin HRM head unit. I've never had to do that with the HRM-TRI.
I wish it were less expensive. After all, it is just an accessory. Sigh. First world problems.
Best Buy was one of the only online retailers carrying the HRM-TRI and having it available. It shipped to me faster than anticipated.