My personal experience of DEGs is that they come to 'work' for NATS already knowing more about the job than anyone else (most - not all). Some are arrogant to the point of disbelief and think that because NATS has a DEG scheme they are the only graduates NATS has.
The process of converting these people takes from a few seconds via a smack in the gob to a few months when they find out just what experience is. Then, on the whole, they are pretty good.
If you come into NATS with the right attitude you will do just fine.