Its difficult to know when pinch to zoom works, and the subscription-based model is poor.
Subscriptions are also overly expensive when compared to other apps: another topo map (albeit with an equally poor interface) is just four dollars, and includes unlimited high resolution downloads without any subscription.
Summary: none Ive found have a stellar interface, but there are much cheaper options out there.
RyanTScott about Topo Maps+, v4.0