It is exactly that. If you knew all of the answers...then there is not much point in anyone turning up! Many people/organisations will both understand and be sympathetic to the concerns of what is possibly a candidate's first selection in aviation [maybe ever]. But to get into any half-decent organisation, you will now need to sit these tests. Just do your best and be honest. There is no emphasis on any one part. All of it is assessed. An example; having spoken to many candidates that sat the OAT/OAA tests in the past - once they had finished - the most common reaction was "It wasn't as bad as I thought and I wish I had relaxed a bit more." (The same goes with airlines and other FTO's).
It is worth keeping in mind that all FTO's are indeed run for 'Commercial Purposes'. However, as has been said: A good one will help/encourage you to get the best out of you on the day and IF you are not up to it then - they have to tell you.
Getting into a FTO is merely the first stage of what is a long, hard process to getting that first job...It is also worth reminding people that aviation is changing at an astonishing rate [Each day -is closer to a systems analyst, than to a pilot, although a good company will pro-actively encourage manual flying], it is not what it once was.
Is it still worth the time/money /hard-work.....that is you decision....for me? Definitely!
Best of luck to all,
Speedtouch.