That's an easy question to answer. NOTHING.
If you have asked to yourself if for some reason your Google Analytics data is going to be compromised you did as yourself the right question. All the data queried from Google Analytics API is directly outputed to your browser, we have take care of removing any caching regarding to your current user's info.
As we're concerned about your data security all the pages within this tool are hosted under a secured SSL endpoint.
If you still have some questions before using the tool, you may want to contact me at [email protected] or using twitter at @thyng, I'll gladly answer any question you may have about this tool.