You get what you pay for. ^^^. I’ll add one more observation: not only do the (narrow, hard & hardly comfortable) seats not recline, you don’t get a regular pull-down tray. What you do get is something that’s about the width of a cell phone. So can’t put a laptop on it.
Bottom line: if you get a super cheap flight that’s not too long, Frontier is OK. In all other cicrumstances, I say, pay more and fly something better, if possible.