I think they've made the smartest decision imo Tom.
Only recently they were close to bankruptcy but now the relationship with Aer Lingus seems to be paying off. This relationship should be left to organically grow, and purchasing craft which are slightly larger and more efficient as well as your staff are trained for is the best option at the moment. Why? Because it offers the best of both worlds to a cash strapped airline. More capacity and lower fuel bills, and without the expense of retraining staff. Once theyre stabilised in a few years, and cash flows are relatively stable, there relationship with Aer Lingus can mean that they can obtain aircraft that can offer greater capacity on current routes, and allow to operate routes further afield that air buses (e.g. German regional cities) could not profitability operate. So give it time, they'll have jets eventually.