The best way to spend bitcoins is by selling them and converting it to fiat currency when the price is higher as bitcoin debit card involves transaction fees and that will make it unprofitable to use it for shopping purpose and even not all places accepts bitcoin debit card at a moment.
I don't think that there is any transaction fees involved if you use them for shopping at offline places and there is only charge if you withdraw money from ATM as it will entertain the charge of 3.5% forex conversion fees which is too high but using for shopping can be useful and handy.