Thx for all the replies, guys. It's been helpful.
I just bought a Polar Unite, a fairly new offering from that company which seemed well adequate for me. Tried it after charging and setting up the app without too much bother or too many expletives.
And so I fitted the thing, or tried to, on my wrist. The strap was the deciding factor before I ever got to switch it on. NFG, total boll*cks, designed by an imbecile.
I expected a high pulse rate (due to the strap), but no. The kitchen clock read my pulse effortlessly at 60bpm. The watch bpm varied from 55 to 105 with no effort on my behalf, it was all over the place.
Tried wearing it on the less hairy part of my arm, underneath. seemed better at first, then that too, became erratic, as did my arm. Took it for a short run and compared it to my Omron BP device.
It was returned this morning.
Felt so let down but I'll get over it.