Fast 100% digestion... I'm not sure whether that exists in the real world (apart from eating a spoon or refined sugar). In fact, I would be interested in any solid studies behind that sort of claim.

With my admittedly limited grasp of biology I would expect that the actual efficiency of digestion depends on a multitude of other factors as well, such as the individual's current state of health, age, rate of metabolism, hydration, climate/temperature etc. etc. All those factors are likely to be working against you in a real survival situation. Not too good to begin with.

But that's a bit beside the point. I'm highly skeptical that an average human could remain active and in good health on a daily diet of a dozen "Survival tabs" for anything like 15 days.

Also, concentrated food is really hard on your liver and kidneys. Even taking meal replacement/protein shakes a little too regularly can have a serious impact on your system. Been there, done that - not good as your doctor will tell you.

In my field experience any sort of highly concentrated food only really works in a very short-term scenario. Anything longer than a couple of days and you're likely to end up with severe digestion issues. Constipation for starters, which is inavoidable if you're getting zero fiber with your diet.

Then, because the concentrated stuff just isn't very filling, you're likely to compensate by overhydrating (if enough water is available in the first place). Which is again liable to seriously mess up your bowels. So in effect, you might easily end up with a bad case of diarrhea. Not something you could afford in a rough situation.

Personally, I'd much rather eat something closer to real food, even if it means rationing the available stock to the minimum. In a 15-day scenario that shouldn't be too much of a problem, most people have enough fat reserves to survive for at least 30 days with no food at all.

BTW, the stuff about Survival tabs being developed for astronauts... Maybe, but I thought astronauts eat primarily real food, albeit freeze-dried or dehydrated rations. So I would take the ads with a huge grain of salt.