[BACKGROUND]I have at least a dozen heart rate monitors for sport use, from the Polar H1 and H10, to Garmin HRM1G, HRM3, HRM-Run, and a Wahoo Tickr X. I wear them for walking, hiking, paddle and racket sports, and gym equipment use. I train daily.[WRIST-OPTICAL versus ARM-BAND OPTICAL versus CHEST-STRAP EKG]• Wrist Optical HR (as on sport watches) is convenient but badly fooled during activities using grip strength due to blood flow disruption. Forget about it for racketsports, rowing/paddlesports, weight-lifting. You need chest EKG or Forearm/upper-arm optical. Cold weather also fools wrist optical as your extremities are the first part of your body to see reduced bloodflow as your body tries to maintain core heat.* Forearm/upper-arm optical HR is comfortable and convenient but requires more frequent charging, and optical HR has "lag" - it takes a few seconds to detect rapid changes to HR like you'd experience for HIIT training.* Chest HR straps pick-up electrical signals (EKG) and have no lag. They don't have to power a band of LEDs like optical HR does so their battery - a cheap CR2032 coin cell - last upward of a year before an easy swap. Downside: a chest strap is marginally less comfortable to many people than an armband. Good strap design can mitigate this. (I have a slight bias in favour of chest HRMs because I can't stand having to charge "yet another device" regularly)[HR STRAP CONNECTIVITY]ANT+ will send HR to Garmin sport watches and bike computers and other equipment that supports ANT+ (Concept2 Row, Bike and SkiErgs), and BTLE will pair with a phone, AppleWatch and so forth. This makes it ideal for fitness apps and ecosystems like Zwift, Peloton and so forth.[THIS HR BAND - The CooSpo HW706V armband HRM]I am absolutely convinced this CooSpo strap is the same unit as the "Biostrap" armband HRM - it's identical in every way except the logo, and other CooSpo and BioStrap devices are also identical. Perhaps they're just marketed through different channels.It offers ANT+ and BTLE connections and I tested using both a Concept2 RowErg and Garmin watch. No problem seeing the strap over either protocol.Since I normally use a EKG chest-strap HRM and was expecting some limitations with this arm-band optical HRM but I was happily surprised here: changes in HR were detected quickly and HR readings were in line with what I'm used to seeing from chest straps. Looking at my Garmin log for the 5k row I just did, I don't see any drop-outs whatsoever and HR is perfectly in line with what I'd expect from the workout.The optical unit this device is built around appears to be the highly regarded Valencell, dual-LED sensor which would correlate with the accuracy of my results - this is the same class of sensor used on many Polar sport watches.Literature for this device claims about 20 hours of activity per charge and my experience with it suggests that's accurate.[ONE GRIPE]I have one gripe with almost all optical armband HRMs: CHARGING CABLES.Almost every armband HRMs on the market - and CooSpo isn't unique here - uses proprietary charging cables and adaptors. CooSpo's isn't bad, being a simple, durable, magnetic two-contact "bar" slightly narrower than the unit.The only alternative I can think of is the "MioPod" which (as DCR puts it "takes the brazen balls award") uses an exact copy of the Garmin standard watch charging cable.[RECOMMENDATION]If you find chest strap HRMs uncomfortable and don't mind charging the device (versus the 1-year of battery life on a chest strap HRM), this CooSpo unit should be high on your list of of contenders. Coospo has used the industry leading Valencell sensor and they've nailed the ANT+ and BTLE connectivity - the unit works without a hiccup.Polar OH1+, Scosche Rhythm 24, Wahoo TICKR FIT are all competitors for this unit but you'll pay more for those. The OH-1+ has reduced battery life and an odd charging clip but can be attached to swim goggles for underwater use. The Scosche Rhythm+ adds "cadence" as a function which make be useful for runners. (most sport watches have cadence already though)4-stars and a strong contender in the armband HRM marketspace but I will likely pick up the MioPod as it's spec'd similarly and takes standard Garmin charging cables.