Pros:
Convenient... plug the reader into the headphone socket at the top of the iPhone and swipe, or if the cardholder and card is not present enter card details.
Mobile... Can swipe a card on job site if necessary, take payment before service over the phone.
No commitment... not tied to a contract on a card reader terminal.
Cons:
not had any yet, it has served the purpose we needed it for.
We have only ever been a cash or check payment business so I am not familiar with typical swipe rates taken by processing agent - the rates on square have never been an issue for us and we get paid quicker than we would waiting for a check.
Customers who have used this were a cement truck company who have frequent hydraulic fluid leaks on new developments and a company who prefer to use a department credit card to get pressure washing service when they need it, rather than wait a month for their in-house maintenance to get to it.