They eat everything except fire ants. Don't know why they don't mess with them, but they don't. They will take the fleas, ticks, wasps, flies, mosquitos, etc. They are better than bug strips.
I have eleven guineas that are lavender, royal purple and pearl gray. They are four weeks old. Just took them out of the brooder box yesterday and put them in a make-shift kennel with a roost. Will leave them in it for four more weeks. (they grow a lot faster than chickens)
You must get them as chics as they are home-bound. If you get an adult and let them loose, they will leave. But know that once you get them, they will most always stay there. So if you plan on selling your house in 3 years, make sure the new owners want guineas. lol
Predator here (I'm in East Tennessee) is the hawk. So we have to keep them covered. Plus, they love to fly. I see my chickens watching them trying to figure it out.