Apple A7SoC and 1GB of RAM gives it enough power - Apple is known from optymalizing hardware to maximal efficiency and same is with this model.
Maybe it's only 2 cores with 1.3GHz but it was more powerfull then most other phones in 2013 and start of 2014. And now it still can be quite interesting option.
Unlocking iPhones is always a little tricky because of method: they don't use code but instead are locked on Apple servers, so thete they must be unlocked to use other carriers freely.
Before using any unlock service for iPhone check blacklist first. If you bought it from previous owner there's chance it will be reported as stolen, lost, damaged or the bills where not paid for the contract.
In our Unlock for iPhone 5S service you can unlock it and also check blacklist to confirm it will be easy or even possible. Prices starts at 9.99 EUR.