Just for the record, I just bought/downloaded and investigated on both ipad, android
-- Galileo Pro which is an OSM product
-- I also glanced at some other OSM products
-- Google Maps (these days has freely download to the cache feature)
-- Maps.Me which is made by a german company. (five bucks)
In all cases you download the app. Then one way or another download the maps, for, the area(s) you want.
My findings and opinion in short:
-- Galileo. Work fine BUT the maps are "all the same color". The map are not clear, ie, large v. small towns are not distinct, large v. small roads are not distinct
-- I glanced at some other OSM products, but they look the same. (Perhaps someone knows different?)
-- Goog Maps. Fine BUT I find the download system is very annoying. You sort of have to scroll to where you want, and then download that: you have no idea what full area you are getting or how much detail. You just want a simple list with items like "download Iceland". The scroll around thing is just annoying, and there's no queue etc.
-- Maps.Me. For me it works. 1, install the app. 2, a list of world countries appear. It says "download which countries?" You just click all the ones you want. it puts them in a normal download queue you can see and downloads them. You get absolutely total detail, for, all of, the item you download.
For example if you download "Austria" you get, as far as I can see, as much detail as is possible with online maps (I'm pretty sure as much as goog. maps).
Note - there is indeed "Iceland!"
{Annoyance: for some countries it breaks down to sub-regaions, which is just stupid. But that's life.}
So for me the "maps.me" product works. I deleted the rest and use that now.
Hope this helps someone.
Footnote: everyone prefers the look of actual Michelin maps. I've bought a few of the Michelin map products (say "France" or whatever), which are, simply, the michelin maps of that country, offline on your ipad. Ridiculously though, they are only the high level maps, not the detailed maps! Almost every comment by purchasors on the app store complains about this. Michelin (I know you're reading), just charge 10x more and make it the whole map.