I first downloaded the iOS version in August last year and reviewed it on my own site then. Because of the size of the iPhone screen, the developers save space by hiding filters and tools on the sides. They are easy to access with one tap, leaving the screen fairly clear. The app is easier to use with the iPad (and Mac) where the larger screens allow the tools to be where needed.
I had done most work with Polarr on the iPad Air 2, but with the arrival of the iPad Pro, the screen size makes this app a really effective editing tool. Different interface adjustments can be made either using a scroll wheel or sliding a finger across the specific panel. A neat Before and After button toggles between the two versions. On the desktop version, there is either the toggle, or the two versions can be displayed side by side.