Most of what Jessica writes here applies more to the "lifestyle" gurus than the productivity ones. But the same applies - some jobs allow the flexibility to work in ways that suit you, and therefore you can use productivity systems, whether your own or from a guru. But many don't. The more honest productivity gurus know this and either don't pitch to people who don't have flexibility or tailor their approach to suit the client. In many jobs that do have some flexibility, the Ivy Lee method is still about the best way of managing work.