Seach Engine Friendly URL: This will change the URLs to look like html pages. Also this means that for each product and category there will be additional page(atleast spider will feel so).So if you do have a 1000 products Your site will be spidered a 1000 times making it get a good rank. The other derivatives to Search engine friendly are SEO ultimate by Chemo ( can be implemented for $40 USD) or SEO-G for enigma (can be implemented for $50 USD)