honestly, with the way their op has been running lately - I would say good call in a less than daily market.

With that being said (for future reference for you and others), Frontier doesn’t really enforce personal item sizes unless it’s so outrageous it’s clear it won’t fit under the seat. Even then, once you get on the aircraft, you can easily stow your personal item in the overhead and the FAs could care less...do it every time I fly them with a slightly oversized backpack.