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.
This site seems to be free to use. I stopped there with my Model 3 twice in March and was never billed for my usage. My car doesn't qualify for free supercharging so I expected the $0.26 per minute or whatever the cost is, but it showed no cost in the car during charging and nothing showed up on my credit card for those two sessions later. But for other charging sessions in other cities on that same two-day trip I was billed as expected.