I think the issue with SPIRIT is if you get one of the older MD80s. The slope of the overhead won't take the rollers. On a flight in 2004 from Denver to DTW, they were making all pax check the rollers when you checked in for your flight. Lucky for me, I had a small tote in the bag that I removed and put my meds and make up in.
Last June on a flight from DTW to MCO, I had to gate check my roller.
pinnie