It’s a high-complexity carbohydrate. The structure is such that it takes a very long time for the digestive track to break it down. For most normal carbohydrates have a regular structure that our digestive enzymes that can break into small pieces by attaching to many different locations on the molecule. With UCAN there aren’t many suitable binding spots on each (large) molecule of starch for them to attack, so it can only be broken slowly from the “ends”.
As an analogy, I’d say UCAN is like burning a candle: slow and steady. Glucose/dextrin, and “complex” carbs like wheat are more like chopping the candle in a blender before setting it on fire: a hot, fast burn.
My understanding is this product was initially created as a medical treatment for glycogen storage disease. Patients with this disease have trouble either releasing or storing glycogen in their livers, so they have very unstable blood sugar levels. Frequent small meals are required, but overnight it would not be so fun to wake up every hour or 2 for a quick feeding. A superstarch lets them consume a bunch before bed without spiking their blood sugar or having to wake up repeatedly to eat because they can eat a lot at once, but the it’s only slowly digested over the next several hours.