I have to add about one hundred users and I would like to not do it by hand. Because my site is a Plone 5.2/python3 one, I guess I could not use collective.mass_subscriptions that in addition seems to have some issues.
I came across the nice way of programmatically create users given in my OP so I wanted to do it but my site is a standalone one and is already in production. Hence I'm reluctant to stopping it.
I plan to this not a lot, but regularly (each year when we have to add new students to our intra/extranet. I guess immersing myself in browser views would be less time consuming than in REST API. So I will probably go that way.
So, only for one site.
Thanks!