There are AOW courses and then there are AOW courses. They are not all the same. An OW diver who has not gotten a solid foundation in basic skills would not be able to pass mine let alone start it. It is possible to fail it. I have no issue with OW divers going with an instructor right after OW but it does not have to be in a course setting. For those who did not get good buoyancy and trim training in their OW course a PPB course may be fine. But they should have been taught most of the skills in that course in their OW.
My feeling is an AOW course should not just be 5 more dives giving a taste of "advanced dives" and is why I wrote my own and got approval to teach it thru my agency. The course is described briefly in my book as far as listing the dives and skills required on them. There are 6 dives with a 7th that could be substituted. Advanced Skills, UW Nav, Night/Low Vis, Deep, Search and Recovery, and Buddy Skills and Assists. Wreck could be subbed for Search and Recovery.
Buoyancy and Trim are addressed on all dives. Buddy SKills and Procedures as well as adhering to safe diving practices are strictly enforced. Separation once is an accident and is addressed verbally. Twice is a fail of the class. Blatant disregard for safety rules is an automatic fail, end of class on the spot, and no option to return.
So the avg OW diver is not going to make it thru successfully. This is why I will just go out and dive with them or take them in the pool. No need to take their money or issue a card. Some choose not to go thru AOW at all. They don't want to go deep or even do night dives. My solution to get them into a higher skill level and build their confidence is through my UW Navigation class. 6-8 hours of classroom, gas management, and 6 dives with HEAVY emphasis on buoyancy, trim, communications, and buddy procedures. No better confidence builder than be given an initial heading, told to make a couple turns, and come back to within a yard or two of where you started. They still though need to have solid basics before starting it.