This discussion has reached a point where it lacks nuance and I'm going to try to fix that.
First of all, some posters seem to be opposed to solo diving in general. I would like to respectfully point out that this is the "Solo Divers" forum, and that if where you're coming from is that solo diving is just a bad idea, then your posts are unhelpful and off topic. I would suggest you share those sentiments in one of the many boards on Scubaboard where those discussions are appropriate.
I would next like to point out that a solo diving or "self reliant" class is not the
sine qua non of a solo diver. There have been solo divers since long before these classes were offered. The actual reality of newly minted divers is that they usually dive under the supervision of a DM. The safety benefit of an inexperienced diver as a buddy is, at best, small, a subject that has been covered in great detail on this forum and elsewhere (and I refer those of you who want cites to those extensive discussions where they are provided). I will also point out that NAUI considers its open water divers to be qualified to engage in solo diving without the need for 100 dives or another class.
And I don't necessarily agree with what I understand is taught in solo classes. I am certain that some are better than others as a good instructor can overcome a curriculum that has weaknesses. But I do not, for example, believe that the mindset should be materially different than for a buddy dive. You really ought to be sure of your salvation (and your diving skills) before undertaking a dive whether or not you have a buddy. Nor do I believe that it is any more necessary to leave a dive plan with a 3rd party than it is when engaging in other routine activities, nor do I necessarily believe that redundant gas should be required for all solo dives, or things like a spare mask carried along. Having a buddy isn't -- or shouldn't -- be an excuse for crap skills, crap planning, and crap execution of the plan. The idea that sloppy buddy dives are OK but sloppy solo dives are not is the grand fallacy here.
I have no opinion on the wisdom of letting an aspiring diver audit a solo diving class. I have absolutely no idea what the contractual and insurance situation is for people who teach such classes. I don't think any of that is especially relevant. Ordinarily in the world at large, outside diving, the act of auditing a class is one of observing the class and reviewing its materials without necessarily doing the work or being evaluated by the instructor. If I were to audit a physics class I would not expect to perform the lab work. If I were, hypothetically, auditing a solo diving class, I would not expect to do the dives, and I would not expect to be able to use my auditing experience for "credit" towards completing the actual class in future.
If there are instructors out there that are using the word "audit" as an excuse to conduct the class without following the rules, well, that's between them and their insurer and PADI and the student. I suppose it's probably a bad thing but it's way down my personal list of Things I WIsh I Could Change About The Dive Business.
So, back to the OP. It is human nature for members of any exclusive group to try to raise the requirements for entry into the group. Basic sociology. The world is full of examples. One of my favorites is the moderators (admins) at Wikipedia, who are constantly raising the "standards" for becoming a moderator despite the fact that they now have a shortage of them. And I think that's what we see with solo diving. Exisitng solo divers all seem to think that new solo divers should be better prepared than they were for their first solo dive. I'm not going to fall into that trap, so I'm going to say:
- Be sure of your skills
- Be sure of your equipment
- Have a navigation plan
- Choose a benign site on a day with benign conditions at first, then expand your limits gradually
- Be mentally prepared to call the dive if you need to
- Actually do gas planning
That's for a buddy dive. It's what you've already been taught, isn't it?
Now, why do you suppose a solo dive is any different?