I have the app on Android on my Samsung S20. It works fine at first. But if I return to the app after a few hours, it will not open and crashes. I've had to uninstall and reinstall twice now (losing my army lists). That is super annoying and needs to be fixed as it isn't currently functional.
Assuming that gets addressed, though, I think the app is fine. I've found some little issues here and there, but hopefully it will smooth out over time. And since I already subscribed to W+ (my son and I are big fans of the animations), it's no extra cost for me.
A couple of main improvements I'd like to see: (1) Ability to re-order your army lists and units within a single list; (2) Ability to re-name lists; (3) ability to change sub-factions (like Stormhosts) without having to create an entirely new army; (4) when selecting a special item (general, artefact, spell, prayer, etc.) for a unit, it would be nice if that info was then written on the unit's entry in your army list so that you could see it all at one glance rather than having to click into each unit.