Being old school, even hand brushes are kind of secondary to me. For free skiing on harsh snow is it even possible to notice the difference?
And for racing, especially a fair to middling U16 how much time are we talking about? Is gaining 0.05s from rotobrushing and expensive waxes really justifiable?
Again I don't have a kid racing nor did I build their soapbox derby cars....
For racing, the kids will be making way more mistakes that cost them greater time than expensive waxes can negate. That being said, while HF waxes might are not necessary being on the wrong (slow) side of the wax temp CAN make a significant difference so one has to get that in the ballpark.
Roto brushes to me are less about race times but instead the time savings and physical effort it saves me when tuning skis. e.g. if I didn't roto, I'd be brushing, brushing, brushing, brushing.....roto gets me to the same base finish just WAY faster.