The original Flixel library targets ActionScript 3 and Flash-era workflows. Before considering it for a new game, check how you would build and distribute the result on today's target platforms. Prototype a tiny level with movement, collision, and restart, then install the output where players would use it.
If the goal is modern cross-platform development, compare maintained descendants such as HaxeFlixel on their own merits. Avoid conflating the two projects. Choose from tested deployment and maintenance paths, not nostalgia for an older tutorial.
Akousa