I had an old Pebble Watch with heart rate monitor – unfortunately the battery was approaching end of life (i.e. watch needed to be charged daily). I went searching for an economical replacement and found a 2019 watch whose price was, was sweet. Ordered one to see how well it worked.
After a week, a second one was ordered for the wife.
You may wish to read this post USING A HEART RATE MONITOR TO PREVENT POST-EXERTIONAL MALAISE IN ME/CFS from solvecfs.org. It does a rich set of links to studies and details methodology.
The BP Pressure is not in most watches, this is a new 2019 model and using newer chips (the endless dropping of cost for features). There is a cheaper one (appears to be identical) for just $16.00.
Having the blood pressure monitor is also sweet (you need to calibrate it using an external BP device- unless you are interested only in unexpected changes).
Having automatic pulse tracking thru the day is sweet. Having BP being available when or after POTS happen is also informative. The cost is so low that arguments about how long will it last, etc… almost become moot.