I bought one of these:
https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1 back in 2021 for £20.
It's a Ztto TC-1 tension meter which works fine.
You can calibrate it yourself:
https://www.bikeforums.net/bicycle-m...on-meters.html
Basically I use it to check the tension is roughly even and to avoid over tensioning.