Down here, we use RSSeo since it's almost an all-inclusive plugin for Joomla!
Now, initially I thought it would pre-populate the meta description with unique content as well as change the titles to pick up some relevant page info, but no dice there.
After tweaking with it, it turns out that it will completely create a separate index (hence the index.php prefix when using K2 and RSSeo) which could possibly pull some link juice away.
However, it seems that all that needed to be done there was just utilize the RSSeo redirects (also included under the Extend option) and all duplicated pages in the K2 index were 301'd over to the index.php portion.
RSSeo gives much more manageability (IMHO) because you can uniquely attribute appropriate meta titles, description and even add keywords (not really big on that, but hey, I'm old-fashioned).
Whatever your choice is make sure that before you install your SEO plugin, be sure that your page was already indexed (if you are not familiar with the plugin so that you won't be penalized by the SE's in case you make a mistake) or if you are familiar with it, plug it in and wait for the clicks to roll on through!
CHEERS!