Then you do the course with a bad instructor for you. A good instructor knows how to teach you with other stuff they don't have and maybe let you use their stuff to feel difference.
What you describe here is a thing you see a lot in sidemount diving and also in rebreather diving: what is the best rebreather or sidemountset?
You get as answer the unit of brand the instructor uses.
But be honest, a lot of other brands or systems also do their work.
I own the REAL Xdeep Stealth 2.0, that is not the classic, that came later, but the real Stealth 2.0. And that works fine for me. Also the newer ones work ok, but I don't see any need to spend money for a new system or wing.
I also own a set from Divesystems (Razor clone), and from DTD/Dirzone. They also work well.
I dive ali80's (or sidekick with ali 80's as bo) and a drysuit in cold water, sometimes water covered with ice. So this will have some negative opinions from some people, but they don't look if the diver can use it safe. They directly have an opinion, without knowing details. And yes, it works well for me and a lot of people around me. No need to move on to steel tanks (I use ali80's as it are also bo's or stages, just move the rigging a little bit, because of cave diving I only own ali80's and no 7 liters or ali40's). All cylinders must be in test, and that is expensive. I don't want to have more cylinders in my house, I own more than enough.
So ask 100 divers and you get 100 opinions.
Then about the always 'do a course advice'. What is wrong with trying yourself? Yes, I am a sidemount instructor, but I am a self teached sidemount diver and later did the instructor course.
Not every diver will be able to become a sidemount diver without course, but there are enough divers who can. I see divecourses in usefull and required as open water, cave, trimix, etc.
Can be usefull like drysuit, photography, sidemount, but also multiple stage cave diver if you are already a trimix diver, etc. If you are unsure, please do a course in the can be usefull category.
And just for fun or interest: biology, sea slug, etc.
You can do trimix or cave courses in sidemount without having done a course, like you can in drysuit without having a drysuitcert. Also there are a lot of instructors who can teach a sidemount course, but never dive sidemount outside a course. So if you want to do a course, look at an instructor who dives sidemount himself in wrecks or caves. Not that person that you only see with a single tank backmount bcd.
Yes, it will take more time if you teach it yourself, and probably you need a camera and/or a buddy to evaluate you, but this can be part of the fun. And remember, gas is gas, so this is not different from backmount. If you don't have trim and bouyancy, you will not have them when moving from backmount to sidemount. And diving with sidemountequipment (that is not directly sidemount diving) is not directly unsafe.
But to feel the real sidemount diving, it must be sidemount diving and not diving with sidemount equipment as you also see quite a lot of times. So if you are self teached/autodidact or teached by a buddy, or an instructor, check if you really dive the way that can be called sidemount diving.
And also check your sidemount diving if you bought your own equipment after doing a course and using rental equipment. Because then it was nice and good during the course, but you don't have the help anymore after the course and setting it up right can take a lot of time. A good instructor can advice you. But you are the person who have to do the adjustments now.
