This is because of the size of the molecule of hbcd vs malto/dextrose. HBCD's absorb quickly due to their low osmolity, but they take a long time to be converted into glucose making for fast delivery yet sustained energy. I love the stuff!
Wasn't this the idea behind waxy maize? Have you used waxy maize? How does HBCD mix up? I got some maltodextrin that wouldn't mix worth a damn.
Waxy maize seems significantly cheaper and touted to have the same effect.