Paying in btc is awesome if you know a little math. Sure the bitcoin is the better option when we talk about online purchases, because it still saves your privacy and some bank transaction fees.
Check your math again... If paying in bitcoin through a bitcoin processor like Bitpay or Coinbase (which is the only option for most stores that "accept bitcoin"), there are two bank transfers: when you send money to buy bitcoin, and when the processor sends money to the merchant.Bitcoin may be more economical than bank transfers for international payments. Otherwise it is just a convenient option for people who have old cheap bitcoins and have decided to cash on the profit. It may (or may not) save some money, compared to selling the bitcoins on an exchange and sending the money to the merchant.
In that case paying in btc for small purchases is completely meaningless.