I think I finally figured out how the attuned ectoplasmator works.
It is not meant to give double xp. It is meant to give increased prayer xp, when killing ghosts only, and the increase is +1 bone tier (xp equivalent to bones => xp equivalent to big bones etc). The official wiki says it gives double xp from demons, that part is wrong. In short, one charge equals one +1 bone tier from a ghost, or one ash spreading.
Additionally, you can recharge prayer with demon horn when the effect takes place (but not if you spread ashes manually).
Wearing the ectoplasmator in the pocket slot will currently not use up charges. This may not be working as it should because it does use charges from the inventory.
Hi
20-Oct-2014 19:22:26