Honestly, BTC is hard to be used comfortably because now it is easily volatile and not stable. Its price is fluctuating all of time. Furthermore, it still has more the speculation. But if BTC can fix all of its shortcoming, it would be regulated and popular in any transaction in the world. Since btc has more advantages by its technology. At that moment, people would feel comfortable using BTC as a real currency.
Volatility is a big problem of transaction. the last time I tried buying on an online mall, It took more than 12hr before the amount of bitcion to be paid was calculated and am expected to pay as soon as possible. More so the transaction took a longer time to confirm. Another problem will be if you have problem with the goods and have to be refunded the price might gone higher or viceversa which might be economically not benefiting to the 2 parties.