not sure what cached means...
I'm not sure I'm using the right term or if I fully understand it myself.
I've got OS Atlas on my phone now.
I can download map areas simply by scrolling around the screen and waiting for them to load.
They are only saved temporarily though.
If I visit that same area a few weeks later without downloading those same areas again beforehand via wifi, they are not on my phone and I have to wait ages for them to download via mobile signal.
I assume that the official OS app downloads them to the phone memory so I have got them permanently, like my photos and contacts.
Backcountry Navigator looks to be USA based and there's no mention of Ordnance survey.
Does it definitely allow you to download OS 1:25000 maps ?