No to BSM and AA. Recommendation, and high grade instructor (most are still graded under the old system, so grade 6 is the highest, would not touch an instructor lower than a grade 5 under the old system).
Some driving instructors are not just ADIs but also fleet trainers (my husband is a grade 6 fleet trainer), which means they are higher qualified.
Then again, recommendation, make sure your son does a 2 hour trail lesson and gets on with the instructor and the way he/she works.
You get what you pay for, cheapest per hour is probably rubbish. Cheapest way to learn to drive in the long run is to get a good instructor. This should also make your son a safer driver, not just pass his test.
Be consistent and take regular lessons, and find out what length lesson will suit your son best.
Feel free to get in touch with my husband if you need more advise (although we won’t know anyone local to you).
Good luck!