In the two test launches shown in the video, the "missile" doesn't fly straight nor does it demonstrate ability to be "guided" by the launcher towards any particular target.

It's also incredibly slow. There are children's rocket kits that fly significantly faster than this.

Yeah, neither article nor the video itself talks about "accuracy" AFAIK, which seems like a kind of important thing in this whole concept, otherwise it's just a "horizontal rocket launcher" which is cool I guess, but not so close to a MANPAD.

The video is also cut in a way so you cannot tell that the launch seems to have been a complete failure? The rocket is vertical at the last frame: https://i.imgur.com/e2Kld6I.png

Baby steps ... with a few more contributors, this could be turned into, say, a $500.00 missile that works quite effectively.

The engine and the warhead are two of the biggest challenges in making a missile, in large part because anything high performance is also going to be spectacularly dangerous to manufacture.

I frankly would care little about the speed; it can always be improved with a better propellant. I would care about a cheap ability to guide the rocket. If it's there, it may be consequential for a real (para)military application.

(A quadcopter is perfectly guidable, but it must be slower than a rocket, and costs more than $96.)