I declined the card with the buttons... Too inconvenient.
I don't mind the card with the printed numbers.
The IB Key app on android is convenient, but they could make it much better. It currently doesn't support finger-print recognition (at least not on my Nexus 6P), so I have to type a pin into it. The app also seems a bit slow/laggy for what it does. You'd think some app that only grabs a challenge phrase and verifies a pin could be very fast... But when opening the app, it takes a few seconds before it's ready.
I'll tell you how it works for me. I login to TWS or Account Mgmt. I select IB Key for authentication and I get a message on my phone. I touch the message and IB Key opens and asks me to use my fingerprint. I place my finger and the TWS logs in. Takes maybe 5 seconds.
I have an iPhone and as I said, I love the IB Key. Too bad Nexus GP isn't supported yet. I know Android is supported as I know someone who has, I think a Samsung, and is just as happy with the convenience.