In reply to vberg:
From what I understand this is very much focussed on the US market...
You're far, far better off with ViewRanger
http://www.viewranger.com/en-GB
you can load the proper 25K maps (e.g. French IGN for Mont Blanc) - only buying the grid squares you need.
It's a fantastic app - and works very well on the iPhone.
But, as with all smartphone apps, their weakness is the smartphone itself as - it can't be used with gloves in cold weather, is more delicate so needs protecting from wet and being dropped, and the battery life tends to be poor (depending on how you use the phone). A dedicated GPS is much more robust (the best units are fully waterproofed), has big buttons that can be used with gloves & a longer battery life.