I didn't see this thread in time to 'vote'. It is a good question to ask.
In a time when there are YouTube videos that cover almost everything (except complicated neurosurgical procedures as far as I can tell), it is hard to suggest that formal 'live' training is necessary. I originally learned by doing - bought a long hose, bought a bungee necklace, tried a couple of different alternate second stage short hose lengths to find the right one for me, and the rest, as they say, is history.
I (still) don't think a class is required. But, I think a business-smart shop would want to provide advice when asked - it helps the customer, opens the opportunity for gear sales, and even promotes future formal training. Of course, that would presume that the shop and staff actually have experience with the configuration, believe in primary active donation, and endorse the approach for recreational diving. As an Instructor, i am always happy to help divers considering a switch to what I consider to be the best configuration.
A question / comment, after watching AG's video: I realize that he is dressed in (thin) street clothes, which may make a slight difference, compared to what he would look like in a 3 or 5mm wetsuit. But, I prefer, recommend, and teach the use of a shorter bungee, so that my alternate is directly under my chin, almost close enough to allow me to move my chin down and grab the alternate with my mouth. AG's bungee is, for me, WAY too long. So, I am now curious - in what position do others dive a bungeed alternate? Mid-chest, like AG, or closer to the chin (shorter bungee)?