I had one, and it did actually build a little muscle. I already had “farm boy” strength, though.
Now that’s a name I haven’t heard in a long time. A long time.
When I was in college, a friend of mine had one. He apparently used it excessively or incorrectly, and managed to tear the cartilage on one of his ribs. He had nothing but vitriol to say about the Bullworker after that. I’d forgotten about that until I saw this thread.
I really developed my brachioradialis using it. It’s prominent to this day. And I had to ask my massage therapist wife for the name of the muscle. Eventually it broke, but I got years of use out of it.