The reply button under each post is used to make a direct reply to the post. The blue reply button makes a reply to the topic itself.
It is also not new.
Yes, @pitaj is correct, there is no functional difference between the self-hosted version and the hosted version.
However, with our hosting, you also get scheduled backups, email support, in addition to us covering the upstream hosting costs. We don't allow shell access for security purposes, but if you have a plugin published to npm, you can install it yourself via the admin panel.
Otherwise, you can contact us and we can manually install it for you as well.