I can tell the difference in whether I'm drinking water or drinking a mix with carbohydrates. If you are riding at a hard HR zone 4 and 5 pace for a while, then when you take that gulp or two of mix, you'll feel the energy coming back within 60 to 90 seconds. And back when I was using fructose/sucrose carbs, the surge in energy didn't last as long. With the maltodextrin that I use now, it seems to be a more steady release of energy that I feel longer between gulps from the bottle. Somewhat seems reasonable as fructose and sucrose are simple sugars where as maltodextrin is considered a complex carb.
If you are only a HR zone 2 and 3 rider, then you may not ever get enough energy deficit to notice.