Reins are necessary, I have two boys with significant additional needs. The eldest is about to turn nine, he is more compliant than his brother and used reins until he was about three.
The youngest is not compliant at all, he also absconds, will not respond to his name and has no sense of danger. We did our first trip with him without reins, pushchair or nappy today. It's been a massive stressful achievement. He was six in January.
Unfortunately I have to tell you that people will openly stare and comment on children with additional needs. With both my children it's very obvious they have additional needs and my younger son has self harming behaviour.
I take advantage of the fact my children's speech and language issues makes it unlikely they will copy me and tell these people to fuck off. Stopping in your tracks and staring back at them works as well.
As my older son has gotten older and more aware I often have a running commentary with him 'look that person thinks we can't hear his rude comments, isn't he rude, I'm glad you have better manners than that' and so on. That works as well. You develop a certain level of not giving a fuck what people think over time.
It will never cease to amaze me that when people see a small child headbutting a concrete pavement over and over again with significant force (he doesn't feel pain like most people do) while a parent physically restrains them their first instinct is to stare, point and comment about his 'bad behaviour'. Someone we saw from CAMHS asked if anyone offers to help, and no one has, not one person ever.