If the feat is supposed to give +2d6 damage for 2 rounds per attempt expended then its a 6. Its better than weapon specialization if you are fighting undead and useless otherwise.
If the feat gives +2d6 damage for 1 round after spending the previous round activating the power then it is unequivocally a 1. There is no conceivable situation in which using this feat would have a better result than not using this feat.
Ideally no divine feat would require extra turning as a prereq. If someone wanted it to power their many divine feats that would be fine but to require it is wrong.
If the feat gives +2d6 damage for 1 round after spending the previous round activating the power then it is unequivocally a 1. There is no conceivable situation in which using this feat would have a better result than not using this feat.
Ideally no divine feat would require extra turning as a prereq. If someone wanted it to power their many divine feats that would be fine but to require it is wrong.