As has been said already, at the end of the day both stage 1 and stage 2 tests boil down to your natural aptitude and whether you have what it takes or not, and this coupled with a satisfactory personality assessment will see you on your way.
A while back in the main NATS selection thread (in the sticky), a poster mentioned that it shouldn't be allowed that failed applicants can re-apply and do the FEAST stage 2 tests again as if they failed them first time then there should be no difference second time, as if you didn't have what it took to pass on your first attempt then its assumed the same is apparent on the second and even third attempt.
Part of the stage 2/FEAST tests involves spatial awareness, it may be worth considering comparing the example of how applicant number 1 has a a natural aptitude for spatial reasoning, exactly what the job requires and then applicant number 2 does not possess the same aptitude but has 'learnt' or 'prepared' it and has no natural ability, rather familiarisation and you can see how further down the line either in selection or during training this will emerge sooner or later and result in disappointment for the trainee.
By all means prepare, but not to the extent that you find you're finding yourself answering questions simply based on familiarisation and not using actual reasoning and thinking yourself, on the spot which is what the tests demand.
Good luck!
