There's nothing wrong with them, I've lived on them and was able to transition back to real food successfully afterward. Some of them I even like---the pork rib, for example, and the clam chowder.
But I wouldn't actually buy them. Through the normal course of my service, I accumulate enough of them for my other needs, like the car trunk and the occasional hunting trip, even the overnight bag if I'm on a weird commercial airline flight. But somebody out there thinks they're great long-term survival food and they want to buy and hold them against Doomsday? Not at seven bucks a meal.
The real punchline, though: they're for sale, to any qualified Commissary customer, though every package is marked in Uncle Sugar's standard all-caps boldface,
COMMERCIAL RESALE IS UNLAWFUL
Hey, I just work here.