CU is a lottery, goalposts changed in the last year or 2, now need all 4's or above in sims leading up to getting approved to join the program. Problem with that is some TRE's seldom give 4's, others give them liberally, standardisation is not their strong point so sim grading is down to the TRE on the day. One may be forgiving of a minor faux par, another might mark you down for it and you only need 1 x 3 to throw a spanner in the works.
That said, if you were in the RAF, then you're in. Once in the program you will see just how unstandardised the process is, some guys getting very simple issues on their command assessment sims, others getting fully loaded and set up to fail.
Ultimately if your BTRE & PBM like you then you should be alright and they can overrule a 3 in order to move you on. If not or you are unsure where you stand with them then it will be made abundantly clear by how difficult it is made for you.
There are some things in Jet2 that are good. The command upgrade process is not one of them.