We have!!! Several times now as a matter of fact. We live in Ligonier, so it's a no brainer for us. It is so much easier than going into Pittsburgh! Just the ease of going through security makes it worth the hassle of dealing with Spirit and their bizarre policies.
Just make sure you do your research, are aware of their fees, know how big your personal item can be and you will be fine. Also be aware that they will count your purse as a personal item, so if you have a backpack and a purse, they will make you pay for the backpack either as a checked bag or carry on. We saw that happen to a woman when we were checking into our flight. Her bag was the right size but she wasn't able to jam her purse into it, so they made her pay for one of them. I have never seen a flight attendant say anything to a passenger about a bag, but I have seen them flag people down at the counter.
Another thing to keep in mind, everyone knows that you have to pay for baggage, but the checked bags have to weigh 40 pounds or less, not the industry wide standard of 50 pounds. That's harder than it sounds if you start out with a substantial suitcase.
We truly have had great experiences. There is a nice restaurant in the airport with a great bar. There is also a little store area downstairs at the gate where you can buy drinks and snacks for on the plane. Parking can get tight, my husband usually drops us off at the door and then finds a spot so we don't have to lug kids and bags through the parking lot.