Some other apps to check out: Locus, Back Country Navigator, Maverick. I use Locus Pro myself, has offline maps, topo shading and map overlays (eg overlay Sat map on topo) as well as every other feature you'd need. Developer is responsive too, I requested the NZtopo maps to be added as one of the online options and he added it.
Full NZTopo50 maps are available for free (my favorite price) I just use the PC program "Mobile Atlas Creator" to make the offline maps I want - NZTopo50, sat, street or whatever. Copy the file to my phone - easy as.
Heres an example of Topo map with Sat overlay (you can adjust the transparancy to suit)
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