I would suggest that because Jet2 are offering 757 positions to none type rated people you can answer a lot of your own questions. They can't attract type rated people because the package isn't quite there and the salaries in no way make up for the lack of everything else.
Channel Express (which own Jet2) has an awful man managment reputation (historically) which it is finding it very difficult to distance itself from. This further makes people nervous of joining them.
Jet2 offers a good opportunity into the jet market but its terms and conditions are years behind most other UK operators.
Good luck with what you decide to do.