Rated 4 out of 5 stars

As I understand - actually it is like sidebar notes, assotiated with web page. Only those, that use this addon and entered the same page probaly can see my comments and I can see their. Is it right?

This review is for a previous version of the add-on (0.43.1-signed). 

Yes, this is correct. But there is more: interesting comments are shown on our website opencomment.org, and we are planning to implement more features, e.g. to correlate comments about the same topics.