A dedicated GPS logger is what you need. You just need a device smaller than your hand and some room for the charger in your backpack. You can import them back to the app later.
You don't need an internet connection to get a GPS fix, so this app would work fine anywhere I think. You then need internet connectivity to sync your accumulated lat/long data back to your account.
Not only you don't need an internet connection to get a GPS fix, but also iPhones geolocation data don't rely on GPS only.
>I think this app would work a lot better for somebody backpacking around Europe than banana boating down the Amazon.
The former may be the exact people the makers are targeting. For instance, my parents usually go on 'package tours' where a travel company takes them around in a group; usually its to Europe, AU etc.
Now you know me.
Incidentally, I spend an awful lot of my year traveling in places where my phone wouldn't get any signal, were I to switch it on. I think this app would work a lot better for somebody backpacking around Europe than banana boating down the Amazon.