A version of the app that works on both iPhone and iPad
Jeffery Lay commented
Although the iPhone app does work on the iPad, its UI is fairly non-optimal. I think an iPad-optimised UI is appealing enough (to me as a user) to hope it's worthwhile for you to develop. I'd pay a few pounds (say, £3? No more than £5.) for it without hesitation. I'd prefer a universal app to a separate iPad app, of course.