My good friend has one of those things in 30-30/.32 ACP. The point of it is to have the capability tp pot small game with your deer rifle when and if needed. We played with it quite a bit and found the point of impact varied a bit by elevation from his 30-30 load. Windage was fine. It was possible to keep it at minute of pop can inside 30 yards. Plenty enough for a possum, racoon, squirrel etc. I can envision several scenarios where this could be a very useful tool.
"A Liberal is someone who doesn't care what you do, as long as it's mandatory". - Charles Krauthammer