Hi,
I write / maintain those tools - and can assure you that everything is handled within your browser. There is no server-side component to the website, so everything you do is just your browser talking directly to the Google APIs. It's 'private' by default - and all the code is on Github if you would like to have a look! Always very happy to answer specific questions though!
Tom (replied earlier) also uses (at DET) a spreadsheet tool that we have that does all the creation and maintenance of our classrooms from our MIS data (it currently works with Arbor and iSAMS / Ed:Gen) - but we use the web tool for any ad-hoc changes as required!
Yours,
JD
