I've thought very little of the flaregun since the pyro update came out.
After a couple of nights playing with flaregun instead of shotgun, I have to say I'm a total convert. This weapon is just lovely. It's much easier to hit with than you'd think, and I'm even liking the slight arc of the flare.
So often, there's a Heavy, a Soldier, a Scout, a Sniper, sitting somewhere that you just can't touch them. But just pop a flare in their direction, and you're golden.
Or you're coming up to a corner - lob a flare at the apex of the corner as you approach, then switch to axe, then flamer as you come round. You're totally prepared for anything which might happen.
So far, I've had the most success with it on Badlands, but it's badass on every map!