No, Giga Impact is not worth it. Though Escavalier has a high Attack stat, Giga Impact provides no coverage whatsoever. Iron Head and X-Scissor are much more responsible choices to take advantage of it's high Attack, even in-game. With a X4 Fire weakness and the need to recharge, Escavalier does not make good use of the move.
Giga Impact does not deal STAB damage with Escavalier either, which hurts the power by a considerable amount.