Spirit has the narrowest seats and smallest seat pitch. Flying 2 1/2 hours for me is tolerable, but my husband complains the seats are too tight. Doubt I would consider a longer flight.
If you don't mind letting the computer choose a seat assignment at check in, that seat is free. If you want to be seated next to family/friend, you can choose your seats ahead of time from $10-40 per seat each way.
You are allowed a personal item to fit under the seat. All other bags must be paid for (even carry-ons). Checked bags have a 40 pound limit (most airlines are 50 pounds).
The airline will charge to print your boarding pass at the airport. Print it yourself at home.
No free snacks/drinks. No in flight entertainment. They sell food on the flight. We bring our own food/drinks.
Spirit is a no frills airline. Customer service at times can be very limited. Spirit does not work with other airlines. I have had good experiences with customer service over the phone.
Add the fees to the ticket price. Spirit may or may not be the best value.
We will only fly Spirit if we are saving a lot of money (at least $400), otherwise we prefer Jetblue or Southwest. We only consider flying Spirit during times when weather/snow/ice not likely to be an issue. Settle any customer service issues before arriving at the airport. Get to the airport early. We don't pay for a lot of bags. We have an Owners Locker. We ship a suitcase to our resort Fedex ground ahead of time (a few dollars more but much less hassle). Pay for bags 2 days ahead of the flight. If you wait until the 24 hour checkin, the price is higher and even worse paying at the airport. If you purchase bags sooner and you can't go, the seat and bag fees are not refundable.