Pros, cheap airfare, convenient flight schedules, direct flights with seemingly shorter times, good in flight service with meals
Cons, charter service, meaning that they can cancel flights at any time and have no obligation to get you on another flight on another airline and won't. They have done this, cancelling flights already booked with minimal notice, leaving the customer scrambling and paying higher fares.
If you can live with the risk of the con, they are great, but there have been many reports and several on this site about flights being cancelled and people left looking for an alternative. If not for this, they are great. I flew them in October and it was a quick, cheap, direct flight, but luckily mine didn't get cancelled.