GrammarFlip is iPad compatible. GrammarFlip was built with a responsive design which means it should work on any device (tablet, laptop, computer, smart phone, etc.). Based on the device, some resolution settings and layouts may differ and may make navigating certain pages more difficult than others.
There is not an official GrammarFlip app right now, but a simple "add to home screen" step on your iPad will do the exact same thing as downloading an app from the app store. Here is a simple YouTube video on how to do just that: https://youtu.be/Mvee2Ct8BTg