I am going to be honest...Frontier ain't good. It's fine if you only care about getting from points A to B and are willing to take some abuse (lol, that's dramatic but it's not far off).
They used to be so great, but in the last 5 years it feels like it has gone downhill in terms of service. I don't know if we just got used to flying United (and we usually try to do the premium classes where more is included) so that may skew our perceptions.
The first was when we were going for a funeral and found out that they broke our suitcase. We had to wait in line for about an hour, they were not going to help us until I insisted. They brought out a smaller/cheap suitcase that we were able to take, though, so eventually they made it right with a lot of persistence.
The next is that the flight attendants were having a really bad day on another flight. We were in row 2, but there was no room for our bags because people were putting them in the overhead space and going to the back of the plane. When we asked the flight attendant and mentioned this was happening (because we had just seen 3 people do it), she said "just put it back there!" and pointed to a free bin about 8 rows back. Obviously not ideal and we had a heck of a time trying to get our luggage when the plane landed. One of the attendants came back and started shifting stuff around and said..."You need to get your backpack out of here!" and pointed to my mom. It wasn't hers, but the FA was just very gruff.
On that same flight, the flight attendants sprayed some sort of Bath and Body Works spray several times in the area up front. It's those smaller, more potent scents that come in the small bottles. It was so bad that I had to do a makeshift mask because my lungs were tightening up due to my asthma. I usually don't have problems with breathing/asthma and haven't since childhood, but that triggered it bad in such a confined space.
They can be very picky about luggage size when you're about to board. Just make sure nothing you have is overstuffed, and they won't try to charge you extra. They will sometimes force people who have a backpack test the size before getting on the plane. If it looks like it is at any point overstuffed, they will charge around $70. The agents get a commission from this extra fee so it incentives them to find baggage that is a little too large. Not sure if this is still happening, but we saw a couple people get pulled out of line to pay the fee a couple years ago.
All this being said, we haven't flown with Frontier since early 2024 and only for a 1.5 hour last minute flight. You will most likely have a non-eventful, fine flight. I wouldn't stress...you might even get a memorable story from it. We now laugh about how absurd some of our flights have been lol