I haven't used those particular flow meters but have played around with the more expensive ultrasonic flow sensors that they're immitating
Only gripe I have with them is that they're fiddly to get right when setting them up on a pipe.
We were intending to use them to field verify EM flow meters but found them to be more trouble than they were worth. By the time we'd mucked around setting them up we would have had the 4 bolts undone and swapped the flow meter for a known good one (and compared the reported flow)
I know nothing about hydronic heating to know if they'd be any good for your application - I live in a place where cooling houses is the challenge not heating them