You always risk the chance that a site will close down and all your content will be lost. In a site like Medium, they have individual weblogs for each member to use. I've seen many of these sites come and go over the past years and all the posts you've written in your personal weblog will be deleted when the site closes. You'll either need to keep a good backup of your articles and information you post on this site or risk the chance of losing it all.
If you are looking to generate an income from your blog posts it is best to post them on your own blog site. This way you can start your own following and attract visitors to your site. On the other site, you may never have anyone read your material, where on your site you can self -promote yourself and attract people to your personal blog site.
If it was me, I would put the material on my own blog site and not a shared site.