Our experience with Frontier was super negative. They had very limited flights from our city so if they had a mechanical problem and cancelled, it could be days and days to get rebooked on another of their flights. We had friends who ended up having to drive 8 hours to another airport to get on another Frontier flight to make a wedding because Frontier couldn’t get them where they needed to be until AFTER the wedding from their original departure city.
There are also tons of extra fees so sometimes it doesn’t even end up being less expensive.
Be sure to see how many flights Frontier funs from your airport to your destination!