I do not believe it is as safe to fly Frontier as it is to fly, say, American. In an emergency, would you trust Frontier flight attendants to do the "right" things? For all their faults, I know the major airline flight attendants are better trained and more professional. I also suspect that the major airline pilots get better training and have more experience.

That said, flying Frontier is perfectly safe. Air travel is crazy safe these days. You don't need to have the BEST crews. So the difference isn't material. So even if it is not as safe flying Frontier as it is flying American, I will still fly Frontier if it is significantly cheaper. Just like I'll rent a Nissan Sentra if it's half the price of an Altima. The Altima is safer. The Sentra is safe.

I've written about this before. It is generally not a good idea to bring a baby wheeled suitcase on Frontier or Spirit. There's something about wheels that makes them want to throw them into the sizer. On both Frontier and Spirit, I've had to abandon suitcases (old cheapo kids wheelies) at the gate because they didn't "fit" the sizer. On Spirit, it was a couple of years ago. At the time, they had an oddball carry-on suitcase size, and they had published their new sizes (the ones they use today) that were going to become effective in about 2 weeks. My carry-on was 100% complaint with the new rules, but missed the old rules by about an inch. The gate agent didn't care. On Frontier, my suitcase was complaint, but one of the wheels stuck out by less than half an inch. She also didn't care. Just bring a backpack. Nobody cares.