When it works well, the plugin is great, but the responsive mode (it's in its NAME) fails after the tabs take up more than the screen width. Check the support thread and see that this issue - the failure of the "more" dropdown to show the rest of the tab choices - has been posted about for several months.
Worse, looking at the support forum on WordPress.org shows that no-one has been answered there in months. Following the provided link from wordpress.org/plugins/easy-responsive-tabs/ for support goes to a page, support.oscitasthemes.com with no support info. Clicking the wordpress icon on that page goes to a list of paid plug-ins. Clicking the forum tab in the support drop down goes to a list of forums but ERT is not listed and searching for tabs or ERT in the search box does not provide meaningful results.
I had to drop this one like a hot potato and my research put me on to a free product where EVERY SINGLE SUPPORT thread was marked resolved. That impressed me, so I went with their product instead.