NDW,
As per Spams post I left the ATC at 17 as a Sgt. Thoroughly enjoyed my time there and made the most of it, as it seems you have done!
The interviewing officers, both at filter and OASC did not question my reasoning behind leaving. As long as you continue to do some activities to keep you busy during your down time, when not studying then I am sure you will be in a good position.