Hi Greg,
regarding the frontend, our plugin is compatible with all responsive themes, as it only allows to edit the HTML code of the widgets, while their CSS is totally handled by the theme, which is responsible for widgets formatting and layout. By the way, we use themes from Studiopress for most of our projects in conjunction with our plugin.
Regarding the backend (widget administration), actually the widget provided by our plugin does not work very well on narrow screens, so it’s not fully responsive. We plan to enhance the plugin in next versions and let it be fully responsive even in the backend. Unfortunately it’s not as easy as to add some CSS media queries, because WordPress uses a weird way to handle widget widths in admin (based on javascript), so it requires a bit of analysis and JS programming.
