rikkyrampage

The top cap only stops rotating because of friction between the top cap and the stem. However, bolt still turns because you are overcoming the friction between the underside of the bolt head and the top cap. In this one-piece scenario the bolt and the cap are coupled. Meaning that as you tighten the bolt, you will need to overcome the friction between the cap and stem. Functionally, it's the same. But the torque applied vs bolt stretch is likely different.

Did you miss the part where Koroyd only works linearly and does nothing to reduce angular accelerations? Wavecel reducing brain injury risk by 81% to 98% sounds like a pretty big difference to me.