I really like Touch ID. I use the American Express app on my iPhone.
Right after receiving my new iPhone 6 in September I loaded Passbook with both credit and debit cards. Apple Pay worked at CVS, the Apple Store, and McDonalds. The simplicity of Apple Pay is delightful. No fumbling for a wallet or card. A finger on the Home Button and, BONK, it is done. An unexpected bonus is the real time reporting of AmEx card usage, even where Apple Pay is not used. It’s pretty slick.
Today the American Express app for iOS is enabled for Touch ID. AmEx got it almost right. Setting up multiple logins can be confusing. For most app logins, one enters the username and then the password. A 1Password user switches apps, copies the password field, and switches back to the login screen to paste the password. This works as expected, but returning to the app login causes the username field to be reset to that used for the last successful login. This requires that the username must be entered again. The work-around is simple — just get the password first. But it is annoying and should not be necessary. The app should not arbitrarily discard user data while waiting for additional input.
Once a particular American Express User ID has been successfully logged on, the game changes. After entering the username touching the password field, the app does not respond to Touch ID. Touching the Log in button with the password field blank is needed to use Touch ID. This is not expected and not what many other apps can do.
The current version cannot connect to an Account Manager login. AmEx says that they are working on it.
Bottom line — Points lost by American Express app for confusing setup, non-obvious access to Touch ID, and no Account Manager access resulting in 3.5 Stars of 5.