Paying by card here happens either by using a mobile card reader, or by just getting up and walking to the cash register before leaving. Much safer.
I was surprised to see in Quebec City that all the stores/restaurants had portable card machines they brought to you. That does make a lot more sense to me.
In Sweden restaurants have started to come out with portable devices and you even have to put in the amount you want to pay (because they want tip which is already included in the price..). I find this really good but at the same time less convenient because I don't want to fiddle with their device.
I would feel much better if I had my cards stored "securely" in my phone and could do "Tap to Pay" over NFC instead and have the waiter bring over an NFC device to tap against my phone.
One more thing that crossed my mind is, what happens if you give this to the waiter, the waiter goes away to handle your payment and it happens to be outside of reach of your bluetooth ping; then you will most likely become worried that the waiter ran away with your card, or you will start ignoring it when it notifies you that it is outside of reach.
While talking about the waiter, what happens when the waiter accidentally clicks the "change card" button and takes the personal lunch on your business card? You might not notice until it's too late and people start asking questions..