I'd never suggest the 10 as it doesn't have any map other than a crude basemap and you can't install other maps to it (well you can but it involves a bit of a faff and you can only have a very limited map). Pay the extra for the 20 or 30 model
I'm not sure I follow what you are saying.
I have the Active 10. It has the 'base maps' that give world wide coverage, I have then bought the 'Platinum' SD cards that give 1:10k, 1:25k and 1:50k. Whole of the UK
They don't 'install' onto the 10, they 'run' on the Active 10.
Exactly the same as the Active 12 or Active 20 (in fact uses the same SD cards)