You can install our site as a web app on your iOS device by utilizing the Add to Home Screen feature in Safari. Please see this thread for more details on this.
Note: This feature may not be available in some browsers.
It needs to be connected in real time. I try not to reboot the Raspberry Pi that I run it on when the cars are being driven or charged to avoid losing data. I'm not getting what the connection is to having premium connectivity though.