We had one experience with them and it wasn't a good one. They were a new airline into our regional airport in South Bend Indiana, so we decided to give them a try. We booked a one way ticket home from Las Vegas last year. Got to the airport 2 hours ahead of time, they checked us in and sent us through security and we THOUGHT all was fine. Got to the gate area and there was a HUGE line waiting for we had no idea what. Found out that the plane we were waiting for to take us to Denver was delayed so everyone in that line knew they were going to miss their connection. We were some of those people also, so we joined the line. The line did not move one person for 45 minutes. While waiting in line, I called the airline on my cellphone hoping to get some answers and alternate information on how to get home. Person on the phone said all they could do was re-book our flights on their next flight which was 3 DAYS AWAY. She told me to keep waiting in line. End of story was we spent 6 hours in the airport that day and STILL had to spend an additional night in Vegas. They did put us up in a hotel and put us on American Airlines the next day to get home. Horrible flight times, but we had to get home so we took them. Got home after midnight the next day.
Called to complain after getting home, and they gave us each $200 vouchers for a future flight. 3 months later, they pulled out of our airport after only being there no more than 3 months. We now have $600 worth of worthless vouchers. I have flown just about every airline through the years and have run into several problems because things do happen, but I have to say that our Frontier experience was by far the worst.