From the inventor:
The first prototype I ever made was with 16 inch wheels but these were too small for someone my height 6’2”. My foot was too big to fit inside the wheel, which was angled like a Landroller, and the axle was too close my foot. The second prototype I made had 20” wheels which were also too small for someone my height and shoe size (although 20” works well with people 5’ to 5’10”). My third prototype was the 24” wheel and that works very well and I would never consider a smaller wheel for myself. A 16” wheel for adults is not suitable, but would be great for young children.
The unique thing about this product is that the wheel is concave so that your foot sits below the axle. The front of your foot is positioned over the wheel where it contacts the ground. Because of this concave shape, spoked wheels are not suitable as they don’t allow your foot to sit below the axle and above the rim. The first engineering we ever had done was to get the wheel made in forged aluminum and it was going to be too heavy, not stiff enough and prone to bending. Any flex means the foot will hit the wheel. Any excessive flex, even if your foot does not hit the wheel, makes them unstable and not easy to control. Companies selling aluminum bicycle wheels issue instructions on how to straighten them out when they bend out of shape, which they would be even more prone to do in a skating situation where there is greater sideways force applied to the wheel. Finally, aluminum 24” wheels weigh about 1.7kg each and our carbon wheels are 800g.
I don’t know if anyone would be interested in skating with 5kg of skates strapped to each foot. I expect that they would be more susceptible to injury. There is also an increase in the gyroscopic effect as the weight of the spinning wheel increases and this would further affect control. At the end of your stride you lift your foot off the ground and reposition it under your body. During this motion the wheel needs to change angle / direction and this would be hindered by the gyroscopic effect in a heavier wheel.
Titanium bike frames are no less expensive that carbon ones and I’m not sure that titanium would be suitable nor how to go about making them in any material other than carbon fiber for adult sizes. For children, who are much lighter, fiber reinforced plastic should be okay.