I had them take it out of the pay and did not give it another thought. The AOG is a great organization that does a TON for the cadet wing. Take advantage of the cheaper rate now, and you will use it when you graduate.
You may be wondering if you will see a deduction in your take home pay and that could be some of the reason for the question. Things could be WAY different now, but when I was a cadet - we had a magic money account.
In 1995, the monthly pay was fixed - as a 4* we got $60 a month ( it is MORE now). You really earned more than that and the overage went into what we commonly called your magic money account. Things like books and uniforms and stuff came out of that fund. When you were about to graduate, you got a check for whatever was left over in the account. It was only then did you see how buying stuff at the uniform replacement store really ate away at what you could have been saving.
For us - the financial impact of signing up for the AOG at in-processing was 4 years down the road and we had long forgotten about it when we saw the magic money check.
Now, you get the money for books in your check and then pay for them out of your pocket. There are a host of other changes to the pay system that are in the cadet's best interest. I don't mean to derail your thread, but wanted to provide insight as to why the financial impact may not be as great in the short term.
Good luck!