I’ve flown Frontier quite a few times,4 hour flights although the last one turned into an 8 hour flight due to a gate hold, then a taxiway hold followed by by a diversion due to a medical emergency.
As far as budget airlines go they are fine with the usual uncomfortable seats and tight spaces.
They have very low prices but offer bundles for checked bags and seat selection and also offer a few rows of extra legroom seats. Maybe take some of the savings and pay for a better seat to make the journey a little more comfortable.
Everything is done via their app and their customer service seems to be a AI . They also lay it on pretty thick about carry on bags and make it seem like you can’t take a carry on on their cheapest fare, you can if it is a regular backpack size that will fit under the seat, larger carry on bags need to be paid for.
You just need to understand what you are getting for such a low fare; or more like what you are not getting.
I’d fly them again without any reservations.