This is an older post, but since I'm implementing Face ID in my Quit That! app, I found it quite enlightening. Did you know that if you implement Face ID, there is a backdoor way another person could access your user's data? Fixing this problem involves detecting if the Face/Touch ID configurations have changed since the last login.
This would be even more important for a finance app. Read on to see how to fix it.
The Missing Step When Using Face ID or Touch ID in Your iOS App by Florin