I agree, even if you had plenty of those Survival tabs at hand I think you'd still feel hungry. The problem with concentrated food is that it's just not very filling. Our bodies are used to getting real food, which includes plenty of fiber. If you're not getting that more or less regularly your stomach won't be too happy about it.

It's a bit akin to basing your diet on bodybuilding supplements such as protein powder or weight gainers. In theory, it should work because those supplements contain all the vital ingredients necessary for survival. But it's a quick way to ruin your digestion. I would treat those tabs as supplements at best rather than actual meal replacement. Heck, even the bad old MRE's would be better, at least they give you something closer to real food.