Conceptually, the Expedition Flare is a flare you launch into the sky to signal a Cenarion Expedition unit to come to your aid. Functionally, the Expedition Flare is a Guardian companion.
Various claims about what it does:
130 damage, 150 damage, 193, 232, and 201 damage (one report, three recorded figures, last was a crit for 402) perhaps indicate that the claim that "the damage scales with your level" are valid.
Reports of the duration vary, but several are very low, seconds, enough for 2 or 3 hits, to much longer, 30 hits reported, and total damage as high as 3800. The key seems to be "for one battle" that you are asking assistance with, does not persist beyond that.