Given my expereience with these as a part of the original test parties when they were originally put into the game. It is a very good leveling option for celestials with relatively easy kills compared to waters. I think they might be a little more expensive but with 1 each it would give a lot of experience, no box required. Again a designated time would need to be set each week for best effect.
With the level limit removed in the most recent patch this might be another possibility.
With the level limit removed in the most recent patch this might be another possibility.