This statement couldn't be any less true today! A majority of the sidemount divers I know are not expedition divers or going through major restrictions. They have chosen that configuration because they like how it feels and they like being able to see their valves.
And a backmount rig requires a back plate and wing, an SPG with 24 inch or longer hose, a manifold, bands (which cost more than a 2nd SPG!). Everything else is essentially the same.
Not really. Besides theres nothing wrong with sidemounting a single cylinder.
What's the point?? That's just a waste of money if the intent is to ultimately be in sidemount.
Most instructors require diver owned gear for tech and overhead courses. I would question instructors that allow rental gear at that level. I have gear for the intro courses, but once a student decides to do cavern or AN/DP, they need to have their own gear. Should something break then borrowing or renting is fine, but testing out new gear while trying to learn a new environment is asking for trouble.