Overview
CF05 is a defensive SMG, reducing damage taken with her Skill.
CF05’s Skill reduces damage taken by a flat amount (similar to how SGs’ Flash Ammo works). While this can be amazing if it reduces damage taken to 0, CF05’s effect is floored at 1 and a reduction of 15 is simply too small to be of much use when the things that usually hit hard enough and fast enough for it to matter (Gunners, etc) also usually have far far more damage than 16.
With her SPEQ, enemies also take 50 additional damage whenever they’re attacked. This isn’t bad, but we already have better sources of these kinds of effects (such as MSBS) these days. If you still end up needing another source of additional damage taken, CF05 can do the job, though you’d likely want to pick better options first.
As such, CF05 is copium to use.