Getting people to eat more broccoli is almost entirely upside. Sure a handful of people will be allergic or whatever, but on a population level some interventions are just one positive after another, and there's no reason it has to be a deal made with the devil.
It really depends on the person, though. They worked for me for a while and don't work now, but I'm a small minority, from what I've heard from people. When they worked, they were great.
It does make me choose more dense meals though since I know I can't eat that much due to delayed gastric emptying. But I have to budget some room for prunes to counteract the constipation. It definitely makes you think about what you eat.
Usually you don't get a free lunch with such a compound.