Decider is pretty good vs AGears and great boss monsters and you can stall with this monster too many turns. I win too much duels for the same in this KC Cup. Another good point is with ECon and with the field you can attack for 2100.
Yes, I'd say decider can buy you some thing, like 2-or 3 turns, perhaps even more until you draw an econ to steal the high level monster or a gravity slash that can be used during dmg step ^_^