I don't currently do them, but I have done them in the past. I think curling is a legit lift, and I don't know why it gets shit on here all the time. Old strongmen could curl ALOT, and even early powerlifting competitions had curls in them.
Since Derek does strongman lifting, having a good curl is important. Sometimes you have to be able to power those objects up with brute strength. I would stil be doing heavy curling, but for some reason it hurts my right shoulder when I curl real heavy. Since I am just powerlifting, I don't need to focus on it. If it was doing strongman, I would find a way to get them done. I just do slow reps with dumbbells for curls right now.
But yes, they are legit, and they do work.