Emmanual at FlexiContent has done an access control addition to FlexiContent that is custom to a site, but it is custom to your site and that means costs money too. He hasn't mentioned if he's going to add that to the open-source release or not.
For SEO, I stay away from anything that says it does it for you. The rules of SEO are always changing and while there are some components that might help a little, it's much safer to just use Joomla's core SEF system. RocketTheme uses Joomla's core SEF links.
SEF is something that there is a lot of talk about, but in all honestly, if you're doing everything else for it that you should be doing, there's less than 1% left of room to improve. Not worth putting your site in the clutches of yet another extension that you have to rely on.
Everyone likes to argue that better looking urls are picked up better by search engines...but things change and these companies work with dynamic sites now...
http://googlewebmastercentral.blogspot.com/2008/09/dynamic-urls-vs-static-urls.html