How different is the actual theory test from the mock tests?

Hi,

Question to those who have already given the theory test.

How different is it from the apps like Theory 4 in 1, etc ? Are the questions similar but not exactly the same ? Or are they very different covering completely different areas of road safety and driving questions?

I am curious because the apps get the question from the theory revisions package that is released by the authority. So maybe the revisions question are different from what come in the exam ?