What i've got from the seo articles i have read so far this issue is totally main url dependant. It should fully cover your product/service in the shortest form. Single words when possible. Good indication of such url is if you can read it in a normal sentence. Good example:
Prestashop-free.com/modules/ogone-checkout.html
Prestashop-free.com/themes/greenhouse01.html
Bad example: (if you decide to offer premium content on such domain)
Prestashop-free.com/free-modules/ogone-checkout.html
Prestashop-free.com/premium-modules/ogone-checkout.html
The issue iam having with prestashop, is that it removes category from product page when you have subcategories:
Prestashop-free.com/
Category -> /modules/
Subcategory -> /payment/ogone-checkout.thml
/seo/etc.html
Product page would result in: Prestashop-free.com/ogone-checkout.html In this example it isn’t that bad, because you are partially covered by your main url. (prestashop, free, ogone checkout). Imagine a site with some random url: ‘prestaproject.com’. In this case removing category is not recommended.