Yes, it is credit card size.
But we can say it is cigarette pack size too.
"CoolBitx is making a hardware wallet that will store bitcoins securely offline", ok that is a fact.
But I think there will be much more cold storages, made by many companys.
Small usb with fingerprint key maybe?
Usb with size like mostly used as Bluetooth notebook adapters (tiny)?
Credit card size is not realy practical and not smallest.
Safety is on the first place.
There will be many secure wallets popping up in the near future. I think some of them do need to add even better security features though for peace of mind. USB sized is a plus as well and I don't think they need to be any bigger.