You could also consider taking two phones. Your main phone would be for everything you need to have on you like for banking and so on. Your other phone could be the one that has the app installed. Could be better than just having a separate user account on your Android phone if you really want to make sure you’re not dealing with any remnants of the software (depends on your threat model).
Without any more context than what you’ve said, I think it’s unlikely that they would ask you to download the app on every phone you own. If they do, it could be time to elevate your threat level in the moment. You may want a backup plan just in case.