Great book! Seems like they had several secret-sauce break throughs.

Seems like if you find an edge, trading on it removes it so others cant see it and copy.

Also these strategies don't scale infinitely. Medallion Fund is closed to investors presumably because they can't deploy that much capital towards whatever the strategy with an edge is.

One interesting bit from the book was that the strategies did not revolve around speed. It's not high frequency trading, or at least wasn't, but much slower moves.