We fly Spirit all the time. Are they perfect?...... Absolutely not. However, from where we stand they do a lot of things right. First and foremost, from Detroit, they offer an abundance of no-stop flights to MCO (and other locations). This allows us to get to Orlando in less than 3 hours fly time. Nobody else does this from DTW. Everybody else has 1-2 stops taking 6-8 hours for what should be a very short flight. As everyone knows, the more stops you make, there is a higher likelihood that something weird is going to happen to your luggage. Spirit removes that from the equation.
Thinking of luggage ...... Yes, they charge for it. However, their personal bag allowance is huge (16 x14 x12) and free and we have learned to pack very efficiently. With optimally sized bags we don't pay those fees. Also, with the $9 fare club, you get $10 off those fees (for each bag).
As for snacks, etc. ...... Because their flight times are so short due to direct flights, we find it unbelievable that anybody would seriously complain about going for 3 hours without a feeding. Now alcohol, that is a different story. Give me a #11, thank you ...... Cranberry and vodka. For $11 you get 2 small bottles of your favorite libation plus the accompanying mixer of choice. If you are going to complain about that price, then WDW is certainly not the proper destination for you.
Their staff is hit and miss in the personality department. We have had some great staff and some that could have used some Disney magic. We just usually brush it off as they are doing the best they can in their particular situation. I know that I would have a difficult time remaining happy if 1/4 of the passengers showed up in their pajamas (yes, they do) and another 1/4 expects to be treated like Donald Trump since they are flying on one of them fancy aero-o-planes. Seriously, just remember that you get what you pay for.
Okay, now for the big bad $9 fare club. We have been members for several years now. Have the $9 flights disappeared? ...... Sure, but so has $2 a gallon gasoline. Now, the great deals all end with the number 9. They regularly offer $19 flights to Chicago......with no extra charges, UNLESS you have to bring a months' worth of clothes or can't make the 1 hour flight without sustenance. Just 2 weeks ago they had a great one-day deal that we took advantage of. 7 of us are booked for $39 flights (each way ... No hidden fees) for a trip from Detroit to ft. Lauderdale. Once there, we will rent a car and drive to Disney's Vero Beach resort where I was easily able to secure a reservation for 4 nights. A nice impromptu trip courtesy of Spirit and Disney that doesn't break the bank. How sweet is that?
The bottom line for Spirit is to be flexible and able to plan well. Don't expect frills, as you won't be getting them. What you will get is the shortest flight possible for a decent price.