They have an entire page claiming that their bike is more efficient than a traditional bike:

https://www.kwigglebike.com/en_US/home-kwiggle-vorteile

I've never ridden one so I'm not in any position to judge it, but the position sounds similar to an elliptical bike.

And this is even more upright, aerodynamics doesn't like to get cheated no layer the size of the wheels. 25 km/h is close to the speed (not quite there, but almost) where people on particularly upright bikes start folding down their upper body to strike a deal with aerodynamics if they need to go faster.

On my standard mtn bike style bike it's just about bang on 27kph where I'm pretty much folded down to do much better. You can't cheat wind resistance.

Due to the swinging saddle you use more muscle groups in your body and there is also more pressure on the paddles.