I've used it; they have a nice system whereby when you buy some paper guides they come with a single use code to enable the guide in the app.
What would be really smart (in fact such a good idea that I'm going to demand a cut of the money when someone finally does this) is to use a kind of pokemon-go augmented reality thing, where you point your phone camera at a crag or boulder, and the app superimposes the topo lines in realtime.
I think this is the way forward for guides, esp given the sizes of some guides these days - keep the paper copy for the coffeetable bog