I have purchased Wiley and Roger phone apps. Each have their advantages and disadvantages; biggest problem is that content to both have not been updated. Good thing is I still feel the vast majority of info is relevant enough to justify their use. But, when it comes right down to it, I guess one is better of with some kind of pad with 4g. That way you could access the Ninja MCQs online, or Wiley. (Although Wiley has advertised that their MCQ test bank is accessible with an Iphone, is wasn't that way a year of year-and-a-half-ago).
.