Ii would say such a transition actually can be really easy, though would have discouraged Simple SEO and instead use either CEON URI or Ultimate SEO... CEON can be setup to indvidually assign URIs to products (thus restoring the short uri while being able to handle any assigned/stored URI that has previouusly existed.) I believe USU has the ability to offer some customization, but I am not quite as familiar with it's overall functionality to provide clear/specific guidance on that, but I suspect that someone close to the software will be along shortly. :)

I would agree with lloyd on dumping the developer. Uri rewriters have to be handled properly in a transition, totally wasn't in this upgrade... A complete shame too...