Reading news reports on line that Spirit is in financial difficulty even after emerging from bankruptcy. I'd be very careful to have a backup plan if planning on flying them.
Sadly, so many will get hurt when this company finally dies. There are so many warning signs, the latest SEC filing really shows how at risk consumers are. These troubles only a few months after exiting bankruptcy is not a good sign at all.
Spirit has filed a going-concern. Not good, basically they project they might run out of cash in the next 12 months.
Have backup plans, watch anything already booked carefully because schedules are likely to change.
Know your rights to get a refund. I think the rule is a 3hr change entitles you to a refund, check DOT. Consider not booking anything more than 120 days out, or whatever your chargeback window is for your processor, as if the airline goes belly up that may be the only way to get your money back. Not a guarantee but a better chance at least.