I wasn't too concerned about the agency aspect of the MPL, because you can effectively offset your training costs against your tax bill. It will take a long time to use up the 100k and you will pay a negligible amount of tax whilst your remain a contractor.
During your time as Flexicrew, you're employed by ARL(CTC) and contracted to Easyjet so you can't offset any tax. Sorry.
BALPA did very well to secure the NEC which guarantees you only spend a max of a year before being interviewed for permanent SO (with the vast majority passing the interview)
To be exact it's between 12-18 months depending on your start date, as Easyjet only issue contracts twice a year. I'm aware of people who have not passed this interview however they can continue to fly as Flexicrew and get another crack at the whip at a later date.