what is going to go wrong:

the mesh network
it is not going to work out, neither in speed, power consumption or protocol.
Mesh networks are very hard to handle.

other technologies
they will be way more successful e.g. Bitinstants Debit Card, they only have to combine it with NFC and maybe some ATM support

costs
you will be eventually better off with a cheap (80Euro) Android phone that offers access to all web services or BitcoinApps than with a ~40 Euro Bitcoin Card (price is just an estimate for display + processor + wireless module + battery + case + assembly + shipping)

bitcoin network
this point might actually work out ... or not. depends on how good the programmers actually are. Problems are the speed of the network (400mb of transactions per month), just calculating/checking one transaction takes about 3sec on such a device. At the time of posting there are 25820 transactions per day ... that will take the device 21 hours to just check them. as soon as you stop checking them for yourself, the device needs a trusted third party to do the checking etc

you would just accept the transaction as soon as you see it in the P2P network (meaning instantly), or wait until a trusted party has accepted the transaction. you wouldn't wait for confirmations in the blockchain for transactions that are lower then the reward for a block.

Conclusion:
I will definitely buy that device if they ever manage to produce it