Following http://wpengineer.com/2044/custom-post-type-and-permalink/ and validating with Tautvidas we concluded there was not reason not to use flush_rewrite_rules() as recommended which is, upon activating and deactivating the plugin.
Following http://wpengineer.com/2044/custom-post-type-and-permalink/ and validating with Tautvidas we concluded there was not reason not to use flush_rewrite_rules() as recommended which is, upon activating and deactivating the plugin.