IMO a waste of time for wizards and maybe others that have familiar spell, if you have wizard spell familiar up and try and use the Lunar Fungus it will tell you that the spell did not take hold and you will NOT get the effect of the Lunar Fungus, EB.
It doesn't work with familiars since this is a familiar itself. However it works for those of us that are pet classes. You will have to choose between this and the previous earring familiar though. You will have to choose the extra regen or the EB.
Lizath of Dragons Justice, 70 Beastlord, Quellious
If you already have a pet up, suspend your pet, summon the familiar, then get rid of the familiar with /pet leave, and unsuspend your regular pet. The buff from the familiar will still be there.
EDIT: It seems that, with at least some familiars, you can summon the familiar even when you have a pet. You get a message saying you already have a pet, but still get the buff from the familiar. I don't know when this change was made, but it certainly is welcome. Should work for any familiar which has a separate buff component. It won't work for the veteran rewards which summon the banker or merchant sine you won't have them there to interact with. Suspend pet first, then summon the banker/merchant, as above.