They are surely "safe". Its just a question of if they are nutritious, or not so much. They are certainly not poison or anything.
Joe, who is a doctor and Tort expert, says they arent great to feed, binds other nutrients or something. I'm rather skeptical of that. Broccoli is in the same family as Kale and Collards, which Joe would say are great to feed. In fact, a small or mid size broccoli plant looks almost exactly like Collards, most non-gardeners couldnt tell them apart. I'd like to see Joe site a study of an analysis of broccoli LEAVES, as I wonder if this has been done. Or if only the broccoli itself was tested, which is much different than the leaves.
Nonetheless, he is almost always right, so if he's wrong here, that would be unusual.
bottom line is they wont hurt your torts, but it seems they might not be a great thing to feed as a "staple" of their diet.