I was finally able to get the Vision app installed, actually.
Had to root my Fire (1st gen - non HD)... which was no easy task because it was running the latest system update (6.3.3). Took about two hours to do between all the reboots. For good measure, I installed CyanogenMod, and then went to the Vision app page in the Play Store and read in the description "if the store says the app is incompatible with your device (it did), click here". Clicked to download, then used OI Filemanager to install it.
The app launches, and appears to operate correctly... but I haven't yet taken it flying, so can't confirm it works 100%.
But VERY excited about being able to use the larger screen, and dedicated WiFi... rather than my tiny phone.