since it's called Tri-Disaster, the effect granted by the attack should change according to the summoned egi.

Garuda - higher damage + knockback/paralyze
Titan - lower damage + bind/slow/heavy
Ifrit - normal damage + weakness or stun
without any egi up - higher damage + bind + either BioII, Bio or Miasma

well the 20second bind sure is useful in some situations but currently it's really uninteresting and has nothing to do with the summons (as Summoner, it's sad really)