What is the function? A movie prop.
That style of knife (Tracker) was featured in a major Hollywood movie ("The Hunted").
To be fair to Mr. Brown, I don't know if he designed the knife before being asked to provide a knife for the movie, or if he designed it specifically for the movie. I do know that I never saw one before the movie.
I never saw the practicality of it. The amount of curvature of the forward edge doesn't look like it would be a good chopper. Nor does it look like the tip would be of any use for things like gutting fish, or any detailed knife work that might come up out in the wild.
I think it's a "solution" in search of a problem that doesn't exist.
But hey, it was in a movie, so I'm sure that alone makes a lot of people think it's awesome, and the most deadly/useful knife design on earth. And that's a good enough reason for them to buy one.
No offense intended to people who own and like them. To each their own.