to answer your question about app stability,
i generally carry a spare device or two; overlander with gaia, samsung tab active-3 with gaia, one or two cell phones with gaia and google maps, and a garmin montanna.
i don't use my garmin watch or handheld c-60 anymore, it is over kill imho.
i have on occasion referred to multiple devices, but only rarely, and mostly because i had not paid for the gaia subscription, a good deal looking back.
i can offer that i have not observed a crash on the overlander device, either with the oem garmin apps (drive & explore) or gaia gps.
the overlander runs the android operating system, a pretty stable OS.
the overlander does not have a bunch of overlapping apps running simultaneously, which i think can cause issues.
tho i think it wise to have a backup for all mission critical needs.
to install gaia on the overlander is easy, removing it probably requires a "factory reset" not sure, just my guess.
1. google search "gaia gps apk" and download the file.
2. connect your overlander to your PC using the usb ports on each device.
3. on your PC use your file manager to transfer the apk file to the overlander, i put the file in the "download" folder on the overlander.
note, i can't remember for certain, but i am pretty sure the overlander will seek permission to initiate the file transfer.
4. unmount the overlander (remove) from your PC.
5. open the file manager in the tools menu, select file manager, browse to download folder, select/open the apk file.
6. after a moment, you will asked "do you want to install gaia app" or words to that effect.
7. gaia icon will appear in the tool menu and you can place a copy of the gaia icon on the home screen.
enjoy.