Agreed it’s a great piece of equipment and also easier on your joints than running especially as you get older, good you got heart and lungs, makes you stronger.
CrossFitters (like me😘) do use it. Our gym does testing on 1k, 2k and 5k regularly to measure progress. Also use them as part of workouts most weeks usually mixed with some weights or gymnastics
I think one of the reasons it’s under used is people don’t know how to use it properly them just on and go way too fast stroke rates too high and are knackered after a few minutes, they don’t use their legs enough either and then think it’s too hard
your time for 10km is very good by the way 👏