RS-Seo is a component-only extension that allows you (amongst other things) to edit the meta-tags in an easy en convenient way. It also creates a sitemap.xml and ror.xml. Nothing new there. It claims to be the first extension that writes a sitemap. Now I can hear people think that the free X-Map extension also writes sitemaps. As far as I know X-Map does not. It just maps the menu while RS-Seo crawls your site and makes a complete map. Very useful, but not the reason I bought this extension. Basically it gives a rating for the search-engine friendliness of each page. After clicking on the page it gives recommendations how to optimize it an it can fix some things automatically and allows an easy fix for many other things.
While I really like it, it is a new extension and it may still have some minor problems. I encountered a small bug in the sitemap. The friendly support crew quickly found it and updated the extension, but other small bugs may follow. It comes with an easy update tool and lifetime support. It is a good extension and may not be perfect yet, but it is by far the best I could find.