I don't get the point of structuring a textbook in this way. It seems like a huge waste of time if you just want to quickly learn some stuff.
If I were a child, I would absolutely detest having learning material wrapped up in a story like that (with the obvious exception of learning about literature itself).
It's the spoonful of sugar idea. I don't use Life of Fred as a primary textbook for my children and certainly would not restrict them to such math books, but some children may enjoy the story so much that they read and reread the books and learn some math almost through osmosis. On occasion my eldest son mentions some mathematical concept, for example Cramer's Rule, that he read about in Life of Fred.
Another series of narrative math books is (Algebra/Geometry/Trigonometry) the Easy Way, by Douglas Downing. They are all available used for the price of shipping on Amazon. You can look at the reviews and see that many people who were surprised by the format have a reaction similar to yours regarding LoF, but a fair number of people like the books, too. I did, and my eldest son did read them at about age 8.
