The Kwiggle's FAQ contains:

- The steering column is made of austenitic stainless steel. This .. even provides a pleasant suspension.

- Of course everyone prefers to ride on smooth asphalt. With the Kwiggle you can also easily drive on paved trails. Even cobblestones are relatively comfortable to ride due to the wide tires.

- Is the Kwiggle suitable for longer distances? The physiologically optimal upright posture and the swinging saddle bring each of your muscles in motion, especially in the hip and lower back area. That's why you can ride even better than with any other bike, without tension, pain or signs of fatigue symptoms. We already rode 200 and 300 km (124 and 186 miles) in one day.

That's referencing their ride around the Dutch Ijsselmeer: https://www.kwigglebike.com/en_US/faltrad-extrem