I cannot agree with the colonel more. I have been in the same position and took some good advice from him. I went to ASTAC which was mainly due to the timing of the courses than anything else as I done it on annual leave.
From what i heard of Cwmbran and my experience at ASTAC i dont think there is much difference between them, ASTAC also have a 270 degree sim due to go live and the instructors and staff were helpful and supportive too.
ASTAC also run a sponsorship scheme where they will pay for your ADI rating. You have to work as a blippy for a bit before hand, however if you have no previous experience this might be worthwhile to get a feel for the job. I dont think the pay is great tho.