I am an enthusiast cyclist and data geek. Many endurance athletes (runners, swimmers, cyclists, duo and tri) athletes collect and train with a lot of data. All pros (as I understand it) train with data – HR is one of the measures – there are lots of others.
In fact, endurance athletes use mathematical models like the TRIMP and Coggan models to guide their training. http://fellrnr.com/wiki/Modeling_Human_Performance
These models incoporate data from sensors to estimate Fitness, Effort, impact of different workouts etc. As you can imagine a lot of attention goes into the devices.
This is a long introduction to set the stage for my reference to dcrainmaker’s website
DC Rainmaker (Ray) is the go to guy for all us endurance sport amateurs. He does lots of reviews of training devices and is the pretty much the trusted source. For example here is his review of the Mio Link https://www.dcrainmaker.com/2014/01/mio-link-first-look.html complete with graphs and stuff.
Over the past years I’ve had HRM straps from Polar, Wahoo and Garmin. Based on Ray’s work I current use a Scosche RHYTHM optical sensor https://www.dcrainmaker.com/2014/05/scosche-antbluetooth-optical.html
You can see one the results of the accuracy testing here
His summary “Overall, the accuracy over the vast majority of the the time is very solid. There appears to be two fringe cases where it struggled, but in each of those cases it didn’t struggle every time. Meaning that I both crossed steel grates more than once without issue, and I crossed cobbles countless times without issue. It’s also of note that I didn’t see any issues with rough roads, which is also common in Paris as oftentimes the road is just cobbles poorly paved over.”
"Overall the RHYTHM+ performs very well on a day to day basis. While at first I was hesitant about wearing it in a non-wrist location, I actually grew to not mind it on my lower arm. And once I moved it to my upper arm, I loved that it was completely out of the way and ‘invisible’.
No doubt the optical sensor market is really just getting heated up. There are a slew of recently introduced products out there – some of them doing well and some of them are struggling. "
Hope this helps and good luck for your search.
(Oh by the way you want R-R recording if you are interested in HRV)