Yeah if that merchant doesn't sell anything over $5-10
Mintchip is for "very small transactions" which is still not a bad idea.
Also you are assuming (lol) no fees. I doubt all these supposed cloud cluster merchant payment gateway ideas floated on their site will do free transactions. Canadian Mint provides the hardware and infrastructure, then all the middle men vultures descend and take fees performing transactions on their network to credit/debit your mintchip. They will contract this out to huge corporations for the most money possible.
There's also the issue of the fine print where they can disable your chip whenever they want and make you replace it, arbitrarily reflash the firmware, ect. Oops there goes all your bitcoins, we're not liable because the mintchip was never designed for it. Sorry
Still a good idea, but yeah I'd rather just find somebody on the street and trade bitcoins for cash with an open source Cryptostick with AES-256 instead of using banks, centralization, tracking, IDs..