Hi FHM
Thank you for your question. I recommend this video on Garmin Running Power:
https://www.youtube.com/watch. Polar has also had a watch since last year that measures this value, which is mainly known from cycling:
https://www.youtube.com/watch.
If you want to collect as much data as possible, the additional info of Running Power might be interesting for you, otherwise the flagships of the sports watch and smartwatch providers already offer a wealth of information for data lovers and those who want to know more :)
I hope this helps you with your decision.
Greetings Darius