Sorry we didn't reply sooner! We use a tiny amount of data when our app is loaded onto your chromecast. Like <1MB, the video itself goes directly from computer to Chromecast so no internet data is used for that, we don't want to foot that bill ;)
Also we've pretty much depreciated these forums now! Future questions will be best emailed to us as we have a support person now to help faster! team@getvideostream.com
Cheers!
Matt