Is it more practical to give these out than, say, crossbows or handguns, though?
What does the range look like, and penetrating power? How easy are they to make and maintain?
Just because we could do something doesn't make it wise.
While true, his odds of assassination go up enormously if he leaves Wulfenburg, full of Hollerzhens, grey wizards and far away from the Black Arcs, to go actively fight at the Black Arcs in unwarded Salkaterns as one of five Hollerzhens on the field. (Discounting the ogre, because you'd need to be mad to try and assassinate Urgdug given the alternative, non superhumanly resilient targets.)
We don't stop our family members from doing dangerous jobs, but I am fairly confident none of those jobs so far have been so dangerous at such a young age, at the beginning of his career. Get some seasoning versus enemies who aren't so adept at assassinations first- a Gor is not comparable to a Khainite assassin.
It's a magazine for a longbow, not a new weapon. It simply allows you to shoot rapidly, without reaching for a arrow to place on a string. You shoot, Draw, Shoot, Draw, Shoot, Draw, Shoot, Draw Shoot, then reload. This magazine would help less trained, slow archers speed shoot. It would not effect their accuracy, or power, or draw speed. It's like using a 5rnd stripper clip for a Mosin vs loading a round after every shot.
If you wanted a higher rate of fire, increase the size of the magazine, this will take longer to reload, so traditional longbows still give you a relatively consistent rate of fire, the magazine increases the speed and volume of a volley by 5x, but takes longer to reload.
This is not a crossbow, or a rapid fire crossbow, it's a magazine for a long bow.
You can remove it, or add it to any existing longbow, so if the manufacturing process is refined, you could have it as an optional attachment to your longbows.
The Magazine is field strippable, made from wood, bone, antler, and doesn't use modern science or require modern science. A engineer inventing this would probably be overkill, as the Ostland school of engineering for all it's drinking is quite advanced.
Craftsmen understand materials, physics, gravity, friction, they might not have the words or the science, but it did not stop Syracuse from building Siege Engines to knock down massive limestone walls, it didn't stop them from building moving towers to fire down on the enemy, and even hook onto the enemy walls.