Bristow are well known for running cadet courses for decades. Most of their experienced Type Trainers and Senior Fleet Captains in Bristow come from graduates of their in house training courses. So, it must work??
I think a large number of pilots on the North Sea, (and quite a few airline pilots) got their first flying job via one of these schemes. With the cost of training today, and the reduction in military spending, it is difficult to see how anyone other than the tiny minority, could afford training without a sponsorship scheme.