For many years now, we have continued to trust "core" Zencart to be technically SE optimised. By this I mean that it generates good, clean HTML with all the page components meeting the fundamental requirements of SE evaluation. It generates a nice H1 tag for any given page, will populate the header <title>, <meta description> and <img alt> tags with appropriate data (which can be custom configured using many variable parameters in the admin panel).
There is really nothing one need do to the code itself to make ZC compliant (technically) with all major search engines.
We have never used these "SEO URL" modules, because while they may generate a URL that a human can understand, SE resultes are always parsed from the header TITLE and the meta description. It will list the relevant url at the bottom of the above, but that is inconsequential...
On other sites where a physical backlink is needed, these are generally submitted as a <a href> hyperlink, into which a readable reference is made ... eg: <a href="mysite.com/index.php?main_page=product_info&cPath=10_11_12&products_id=11">See our fine cupcakes</a>
Again, the nature of the href is inconsequential... The text used for the hyperlink is what's important.
Perhaps to illustrate the folly of "SEO URLs" and their completely unnecessary generation, we completed a website for a UK client just 5 weeks ago.
Today, he is achieving top spot on Google UK for practically ALL of his vital keywords. YES... in just 5 weeks!
Test me out if you don't believe me. His site is HERE...
Go to it and grab a product title off his site... any one. Then enter this in Google UK and see where he features in the results. In the vast majority of cases it will be in the top three - more often as Number 1.
We got there by TRUSTING CORE ZC to technically deliver... and by focusing on the nature of the content composition of the site.
Believe me... there is no need for any "SEO URL" nonsense on any ZC site.