Google Charts is hosted, like https://app.chartblocks.com - you can download or save the charts that get produced but it's not a charting library that can be used offline. If you want hosted charts you've also got to give someone access to your data.
For me, the fact that I couldn't use Google Charts offline was the end of the road of "testing" GC. I needed to make an intranet web app that would not be "allowed to communicate with the exterior".
In my experience, Google Charts (along with everything else out there) will have you begging to pay for Highcharts as soon as you run into something slightly non-standard, which happens quickly.
