Merchants may frown on the use of a card that does not depict the financial institute, that issued the card. Would you accept an American Express Card that wasn't clearly indicated on it? Would you lay out your information on an Apple or Android based system, that someone else or someone else's card could snatch, and then use on your behalf that didn't have your signature visible or security code written on it? This is a no sale.

I'm not quite sold either. Will the credit card companies honor user's insurance policies for non-authorized purchases? I'm also curious as to what sort of security is built in to (1) make it unhackable and (2) keep sneaky restaurant employees from doing 20 quick scans of customer's cards each shift.

My wallet can easily accommodate 5 or 10 cards and the convenience of morphing them into one may be worth about $1 per card...$10 max if you have lots of credit...but how many will are willing to pay money in exchange for shuffling cards? I have little problem selecting a card according to color or design, but mostly use one card, and on rare occasion need another. This a solution to a problem I don't have.

It seems like it would be easy to lose one card than if one had separate ones. If one has the information on the phone as backup, why not just use the phone?
I wonder what will be next? Having a chip with all that information implated in our forhead or hand? I heard that some are already doing that.

"My wallet can easily accommodate 5 or 10 cards..." Mine can too, unfortunately my pants pockets can no longer comfortably accomodate the wallet once I have loaded it with so much junk.
The original cards you currently fuss with are less secure than this device. If you have an RFID (contactless) card anyone with the right equipment can collect your card data from 10-15 feet away as it is completely unencrypted. The swipe cards can easily be reswiped or a card scapper can be attached to the devices you use like ATM machines and point of sale devices. The only protection you have is the banks insurance policy.

In principle this sounds like a good idea. But as in all things made to be techno-convenient, clever hackers will find a way in. Then instead of losing one card, you've lost them all at once.

The Wocket, if it ever ships, solves the security problems and also can function as your entire wallet.

I think the idea is cool. I only have a debit card and no other credit cards, but I hate all of the store loyalty cards you have to carry. I wonder if you can manually enter cards such as medical insurance or prescription cards that don't have a magnetic strip?
In North America in the next 12 - 18 months, all credit cards will be re-issued to the new embedded chip credit cards. I didn't see anything to deal with that.

Just to follow up, from the FAQ section on their web site:
Can I use my Plastc Card in a Chip and PIN machine?
Soon. Every Plastc Card comes with a deactivated chip. We’ll be sending out an over-the-air firmware update shortly after the product ships to enable the chip and allow you to use your card in all Chip and PIN (EMV) machines/devices.

This card could be used by someone to "borrow" another's cards, copy them onto his Plastc card, and then return the cards to their owner, without the latter being aware of the "theft."