It's claimed to be a useful device by every manufacturer who made a version.
The concept of the tool is to function as an anvil for knocking rivets out of a knifebar and riveting new knives into place. The 3 slots on the right are supposedly very useful to take wows out of bent bars.
Reality seems to be a little different from concept though, and most discussion of these devices I've been involved in or overheard usually involved some dang fine cussin, a bit of hammer throwing, and replacement of the "tool" by a rock or hunk of railroad iron.
My personal preference always went to a 6" chunk of rail with a few appropriate holes drilled in it.
You often find these "tools" in 2 or more pieces indicating some farmer delivered a fatal blow with a large hammer.
Sometimes you find them in rich people's houses with felt pads on the feet and all painted up. I have no idea what purpose they serve there.