A Brookfield contract may or may not be offered to you after your initial 6 month training contract with Ryanair.
If you join as a cadet, you'll do your 6 month training contract (or realistically more like 3 months) and you'll then be offered a position as Ryanair crew on either a Ryanair contract or Brookfield contract. With either, the job security is more or less the same - you're on a 3 month notice period.