bought one ages ago, even the super gentle slow inversion in the demonstration video causes sheets to slip back notches on one or both sides, some films are worse for this than others. In reality it is a 2 sheet holder, not a 6 sheet, do not load 6 sheets. And load them on the inner most sections so they dont slip off the reel altogether and scratch.
That still happens with gentle side to side twist agitation too, or at least when you drain the tank. Gentle twist agitation works fine for C-41 I've found.