They were terrible, so I was glad I had a backup vegetable.
I nibbled one when they were still raw, and it was interestingly pungent. So I tried the "quick-steam" method, which supposedly preserves the assertive taste.
After the recommended cooking time, they were still very fibrous and they tasted like... leaves. But really bitter.
So I said, well, they're not going to get less palatable, so I switched over to slow braise. Added some water and quite a bit of beef bouillon and cooked 'em for another half-hour while we ate dinner, then reduced the liquid down to almost nothing. Sprinkled on some sesame seed oil, and a little bit of lime juice, and when it cooled down to room temperature, it was actually something I would eat voluntarily. Still somewhat bitter, but not in a bad way.
Took them as part of my lunch yesterday, and they were fairly tasty, but I don't think they really agreed with my digestive system.
Given all that, and that they were a fair amount of work to prep for a very simple recipe and that all the recipes I've seen for greens included lots of caramelized onion or bacon or other things that are yummy on their own, I'm thinking that I may have to put them in the "not actually food" category...