It didn't enter the (western) human food stream until the 1930's forced by a food chemist. It's a new food, my great-grandma would have called it cattle feed, so I'll get mine after the cows have finished processing it, thank you. One local grass-fed producer puts his cattle into a field of it from time to time. Probably as good as any other grass.
With a little more research I see that it is totally indigestible by humans unless juiced to remove all the cellulose, the claims of B12 come not from the grass itself but the microrganisms that grow on it. The juice is 70% chlorophyll which I don't think is any benefit to humans. I'll stick with spinach. That is much closer to the leafy greens that Grok would have found.
Sorry, I don't mean to be harsh, it just seems a bit like snake oil to me --- on the other hand snake oil might be good stuff -- high in omega-3 animal fat. Very primal.
It's grandma, but you can call me sir.