A great read explaining a complex practice. I do not buy the criticism of the book, which basically boils down to "everyone has always tried to game the system on Wall Street, and investors are far more ripped off by brokerage fees than any HFTs." That doesn't make the practice any less unseemly to the outsider, it is just a very modern example of how financial types can make billions without adding a cent of value to the economy at large, just by exploiting informational access.