Yes, I think it is easier to use an external battery charger with a built-in battery to charge a smartphone or tablet battery because you don't need to find a power outlet like a USB power brick style charger. Some external battery power chargers even have a Micro USB cable built-in, so you don't need to carry an extra cable for charging.
External chargers could be good if you live in places with tornado, tsunami, power outages, and unreliable power since you can buy many of these external chargers, and charge them all up, so you have enough power to last you many days to weeks.
