I've tried it briefly (so far) and it seems like a well thought-out and developed app especially if you already are use to the Nik style interface with their full programs on the computer. It combines elements of Silver Efex Pro, Viveza 2, and Color Efex Pro and offers various presets. There is a bit of a learning curve to master all the gestures that control the various settings, but it is pretty intuitive and shouldn't take too long to master. Control points are featured, as well. I am not so sure that the iPad will ever be the predominant choice for serious editting/post processing, but for some basic stuff, it works pretty well and the process and results can be both fun and productive in many respects.
I agree that it'll probably be a while before an iPad app will be a "serious" photo processor, but for a quick camera-to- social media workflow, it's hard to beat the convenience. Recently, I've used an Eye-Fi card to push photos from my camera to my iPad, then did touchups in PhotoGene and other apps, and finally used iLoader to push the photos to Facebook. Not a laptop in sight and no cords!
Just thought I'd give this product another as I've spent a fair bit of time processing images with it today and love the simplicity of it (as well as the results). I don't use it often, only when away from home, but do enjoy it when I do. I don't think I'll get the recently released Mac version as I'm also very happy with Nik's PS plugins.