thank you both for your replies. You are correct on it being a fast moving industry (my day job is working with iPads and apps in another sector and it is hard to keep on top of!).
It is wise to have chosen a reliable platform to deliver your content and I understand the limits that this may have imposed.
I have downloaded the app and the sample issue and found it worked well; if it allows you to have additional content (audio or video) such as the Wired app provides then this can only help move the magazine forward.
It is certain that as soon as my eSub expires I will switch to the app based subscription.