Over in "Rank the Bars" you asked why ProBars aren't a favorite. I can tell you why they're
not My favorite -
The first ingredient is sugar. The bars are ~45% fat. They cost $1/ounce.
PowerBar's Harvest line, for instance, has Oats first, Fat is ~18%, and cost is ~$0.50/oz.
Complex carbs are easily digested "on the run" versus fats. In half a ProBar you get about 100 calories of carbs and 80 of fat. Hiking at 300 calories per hour (and sometime a Lot more) you are operating in "deficit mode".
RTFM should be RTFL - Read The Friken' Lable ;-)