They are great for pigeons in buildings if you have a smoothbore .22. I was hunting pigeons with a fellow this summer who uses one. He goes inside the building with that, and I stand outside with a shotgun. We killed over 800 pigeons out of one building last summer, and he certainly took his share, so I'd say they can be quite effective. So far he has been using the savage single shot, but he is supposed to be getting his remington pump soon.
We also have a trap thrower of sorts at our gun club. It's basically like the ones for handthrowing clays, but this one throws crackers. Just make sure the crackers are dried out, if there is any moisture it just pokes holes instead of breaking them.