There are two things.

First the supposed "greatly improved lateral stability".

How would this suspension do that ?

Because this dual spring is wider than a single suspension ? That's pure b...ls..t because the frame side is connected to the frame in one point with only a hook.

Second, what's the difference with the original spring+PU+foam ?

Both are spring based, the Kamoya seems to have only springs in compression (the PU is in rebound, note that the two video and the picture show slightly different suspensions) while the original has spring+PU+foam in compression, so not better (the Multi-S has a real damping).

And this Kamoya has the same problem as most other third party front suspensions for the Birdy: the spring is shorter than the original one what makes it less progressive.

What I see in the video is... what I see when riding my Birdy with its original suspension, a spring that absorbs the road roughness, no evidence that it does it better.

Note that there are two springs for the original front suspension, 8.5 turn hard and 10.5 turn normal stiffness and two foam stiffness.

The reviews both show an old Birdy model, not the current one (BTW. I saw the same concept of front suspension mounted on a Frog, the now discontinued old little brother of the Birdy).

Last point, with two springs, two big rods inside the springs, two assembling thick aluminum bars, this suspension (like the Kamoya suspension for the Brompton) must be very heavy, much heavier than the original one.

I spent enough money in third party components for Brompton and Birdy that appear worse than the original one and some of them so badly designed that you wonder if the seller/designer ever tried to mount its component on a Brompton or on a Birdy !?