Thank you all! It is just a experimental concept, but inevitably the question of how it might actually fit into ancient warfare is raised.
Here is my reply to a certain someone that goes by "Lloyd":
It is indeed a device that sits a little awkwardly between javelins, bows, and slings. I believe that if it were to be deployed, it could be given to slingers to train with, to replace the heavy stones (~350-450g) that were used against heavy infantry. The slingers will already be deployed in such a way that they have room to use them, and while the darts are a bit more expensive, the reduced weight, greater range, and increased terminal effect that a 200g dart could provide over a heavy stone, could perhaps give it a worthwhile place in the army.
As fellow slingers, what is your opinion on this notion?