At one time the installation came in the form of an xapk file, hence the instructions.
After that, returned to the form of the classic apk.

As for your device and NDS, it does not matter that your installations are on the card, they will be fully installed in the system memory of the device.
With NDS, you can't choose a location for maps, but the software is smart enough to see how much system memory you have and transfer content to the card when you have it.
Of course, app should be allowed full card access before launching and downloading maps.
Make sure the card is fast and high quality enough.

TT GO, although an older app, is still very good. If your device is mostly offline, then it is the most suitable.