Was using Ultimate SEO 2.105. It took some trial and error to get it working correctly, but once it did, it was great. One problem: it doesn't change EZPage URLs, and we have a lot of articles on our site posted with EZPages.
Removing Ultimate SEO was a bit tricky...you have to remove all the files it adds:
admin\includes\extra_datafiles\seo.php
admin\includes\functions\extra_functions\seo.php
admin\includes\reset_seo_cache.php
includes\auto_loaders\config.ultimate_seo.php
includes\classes\seo.install.php
includes\classes\seo.url.php
includes\extra_datafiles\seo.php
Then remove the chunks it adds to:
admin\categories.php
admin\product.php
includes\functions\html_output.php
Then remove the database tables and columns it adds. There's a function called uninstall_settings() in includes\classes\seo.install.php which you can grab the SQL from to do this.
The remove all the rewrite rules in your .htaccess file it adds.
Once done, I decided to try Magic SEO URLs instead.
PROS:
• Installation: truly a two-minute, painless procedure. I like that it only adds a single file to your zencart folder.
• Support: Impressive. When things didn't quite work as expected, I was very pleasantly surprised to find the vendor very responsive, even FTPing into my site (with my permission) to diagnose a misconfiguration at the webhost, and devising a workaround.
• Changes addresses for all pages, including EZPages, Define Pages, etc.
• (When properly configured) won't allow more than a single SEO-friendly address for a page, and redirects from any variations it recognizes to the correct address with a 301. Ultimate SEO URLs allows an infinite number of possible URLs as long as they end with the correct category/product/etc. ID.
CONS:
• Closed source, pay-for add-on.
• Documentation: very brief instructions for installation, nothing else.
• Adds a link to the Magic SEO site on the bottom of your site pages. Can be hidden with CSS, and if you insist, the vendor will send you another copy of the add-on with it removed.
• When the add-on didn't work with my custom 404 page, as the vendor said it should, he threw it back to me to muddle with the rewrite rules to get it working.
I also tried Ultimate SEO URLs 3.0 beta. Also impressive and quite possibly a better deal than Magic SEO.
• Installation: copy lots of new files, edit various existing files, try adding a couple different chunks of rewrite rules in your .htaccess and see which works.
• Documentation: Extensive but not yet complete.
• Various "URL Plugins" allow you to enable/disable URL rewriting specifically for products, categories, EZ pages, review pages, search results, etc.
• Must enable the "Core: Default" URL plugin, or links to Define pages (Contact, Sitemap, Unsubscribe, Privacy) don't work.
• Can choose the file extension: nothing, "/", ".html", etc.
• Can strip out invalid chars from URLs, convert to lowercase, etc.
• Like version 2.1, still allows infinite variations on URLs, exposing your site to potential duplicate content penalties.