The FMD is very good. Definitely read the book so that you can fully understand the lifestyle and the reason why you eat certain foods on certain days.
I use the app but it is not updated to reflect the most updated food list, recipes from the cookbook nor is the portion sizes accurate.
I have contacted tech support in regards to the updates and I was informed that the nutritionist/author Hayley Pomroy does not own the app.
Lets hope it can be updated sooner than later.
The Study of ACTS about The Fast Metabolism Diet, v2.9.2