They show ones tethered to a shipping container, which is like 10x less area than a wind turbine base. But since the kite has to be released in an arbitrary direction and has to be able to land in a somewhat arbitrary location, the de facto land area is probably much larger. You don't want the kite to land on top of a sheep or a solar panel.

Portability is probably true but kind of niche. Most of the time you want power generation at the same place for decades. Maybe these could serve as emergency power generators, but with them being dependent on the wind you can't rely on them for emergency power either, which means you still want other forms. So all the kites could do is provide emergency power in situations that would be okay without power.

Maybe nomadic people could carry a small one with them. The video also mentions putting them on ships, which might honestly be the best application, saving a decent chunk of fuel if the ship happens to be going in approximately the same direction as the wind. (Though you would need to replace the engine to make it a hybrid).

As for them being cheaper, I could see the material costs being lower, but with all those quickly moving and torquing parts I would expect them to wear out a lot sooner. They can also crash into the ground quite easily. They take a lot more labor to set up and operate, even if you trust its steering software not to crash the kite (into something important) once it's up there.

Another factor with cost is the amount of waste they produce. Wind turbines are mostly metal, which can be derusted electrically. Meanwhile these kites seem to be mostly made of plastic, which is a form of unburnt fossil fuel that sheds poison until you burn it. Plastic is cheap in the current pro-poison economy, but it shouldn't be. Also non-poison materials tend to be heavier that might make the design less viable and less portable.

Still, they could make sense for 0.01% of power generation by kWh or something. Putting them on ocean-faring ships seems plasible.