Google Wi-Fi according to the Google Wi-Fi support page, does not track the websites you visit or collect the content of any content in your network. However, the Wi-Fi collects the info about devices collected, channels, and data usage for optimization of the device and network. In addition, once you download the app, you can opt out of the data collection points indicated above by configuring your privacy settings. This way you can be sure that the Google Wi-Fi and Google Wi-Fi app, only collect data that you allow them to.