I take Ritalin after a diagnosis in my 20s. I don't have much to add that hasn't been covered, except on the issue of coping in mainstream school. Superficially I coped very well - top of the class, didn't get in trouble, had friends.
But I was also constantly the target of bullying, because I didn't quite follow some of the subtleties of social interaction, and could lose my temper and say the wrong thing on impulse. This in turn would make me absolutely terrified of social interaction out of fear of saying the wrong thing.
Teachers let a lot of low level poor behaviour slide because I did well academically, I was a girl, and they knew I'd never escalate beyond minor infractions.
I coasted by academically because I have a very good memory and high IQ. In a structured school environment I did very well, even though some days I wouldn't do a single bit of work all day. I also figured out my own coping strategies very early on, eg keeping my hands busy when listening to lectures.
Out of school I struggled. My university lecturers did not take kindly to my seeming inattention in class, or talking out of turn, it was seen as arrogant and rude. I gave up my post-graduate studies because I could no longer keep up academically, I physically could not complete all the reading, I couldn't plan or structure my study time, and the bullying continued even in that environment.
But for me the worst parts of being undiagnosed and unmedicated were the things no one saw. The anxiety that felt like my insides were frozen, the constant insomnia, ocd symptoms, and above all the feeling that deep in my core there was something wrong with me, that I was not as good as other people. That my difficulties were not due to a diagnosed disability, but rather that I was fundamentally broken.
You sound like you are a fantastic and caring Mum, and I thank you for taking the time to seriously consider what's best for your child.