Custom tea shirt scripts

I have been looking for a script that is not to expensive that will allow clients to design there own t shirts but most of them are very expensive, however i just came across this plugin for Opencart
http://codecanyon.net/item/opencart-...029?ref=baby2j
Having never used open cart could someone who has post how easy it is to add to an existing website or is it stand alone only and if anyone has used the plugin if it is any good, thank you.