Quite honestly, the internal process is much much harder than the external DEC application process. And it is completely dependant on the base captain and the TRE doing the simulator and interview. Some do 4 hour interviews for the very first step, others just take 5 minutes. So it is not really standardized at all, it is very much a personal preference of those doing the interviews. On the other hand, the training is just the bare minimum and will not do much in terms of training at all, so better study up beforehand. For an external FO, one is at an distinct disadvantage against the internally brought up cadets who know the books quite well and set the standard.