Read Here, and remember that you are reading information put together by a marketing company. It's good info, just a bit slanted.
No fiber, no protein, no fat. Does not sustain life.
But in powder form - Perpetum is a light weight way to carry a lot of calories, plus some protein, a few electrolytes, and other stuff.
"Malto" buys 50# bags of the base and mixes his own. And he eats "real" food as well.
Some UltraCyclists use malto exclusively for coast-to-coast racing.
It's not for everybody, but if you are a competitive distance person, it has a place.
Personally, I like Lays potato chips (repackaged from a can) and Chex Party Mix. Add 4 or 5 PowerBar "Harvest Energy Bar", or ProBars, and it is easy to eat 1800-2000 calories while on the trail. Then use dinner, a 2 AM snack, and breakfast to round out calories, protein, minerals, vitamins, fiber, etc.