This is so not as useful as you might think. While these might be okay for small transactions, like less than 20$ - they are not at all suitable for larger values.

The grand problem: There is no way to verify the bitcoin really is on the key. In the end you are having to trust that a piece of hardware is what it says it is; no the little punch-out does not count. This is different from a hardware wallet in that you are not simply trusting another device to do key signing for you, you need to trust that this device really does contain bitcoin.

Of course this can be done at POS using the blockchain, but that is not offline now is it.