I’ve never cooked that cut of meat (or, even heard of it until now), but my guess is that there’s very little fat in it, and a LOT of connective tissue. The neck muscles are pretty hard-working and don’t get much rest.
I suspect the butcher that came up with that cut likely was looking for a way to make a bit more profit than he would turning that muscle into hamburger.
Thanks for reporting your experience. If I run across that cut of meat in the future, I think I will pass.