@Chameloshi: Range will be limited by the viscosity of the liquid you're firing, which for LN is pretty low.
It's mainly impractical because flammable liquids store more easily and for a lot longer.
Also they stick to you, LN tends to bounce off.

@Ijerk: Well, flamethrowers don't usually have long range anyway, and it doesn't really take long for LN to freeze things. And since LN is just supercooled nitrogen, it should be easier to create than flamethrower fuel, and more common.