Don't be fooled by getting cheaper tickets, you will pay more for your luggage anyways, either check in or carry on.
Not to mention the worst possible customer service I've ever experienced in all 3 airports I went to. Not only were the people at the check in rude and unwilling to answer any questions I had, but when I simply asked a girl at the gate when my flight would leave (my flight was delayed 4 hours because of issues with a door not shutting properly, not anyone's fault) she rolled her eyes at me and mumbled "Don't know...". I understand some people might not like their job, but being rude to a customer is not acceptable, especially if I'm being nice and understanding about the situation.
I would rather pay more money on US Airways and have a more enjoyable experience than ever fly with spirit again.