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 currently requires accessing the site using the built-in Safari browser.
The CAN bus is available at the diagnostic connector in the passenger footwell, but the product you mention is designed for the Model S. The CAN messages are different in the Roadster, so you would need to be able to modify the firmware in the controller of that device (or get the manufacturer to do that work given details about the Roadster CAN bus messages).
The CAN bus messages in the roadster are different than the Model S. The manufacturer would either need to modify their product to support roadster CAN bus message format, or you would need to build and write code for a convertor box to modify the signals to match.
The publicly available info on roadster CAN bus messages (instrumentation bus) is here:
A reverse engineering tool for systems based on CAN bus communications - openvehicles/CAN-RE-Tool
github.com
However, that product may be better of listening on the CAN bus the motor is on, as that may include more power related information. There isn't anything publicly released on that though.