I believe it was literally just added in a patch yesterday or the day before.
It’s essentially a replacement for eating and drinking for out of combat healing as you can’t just eat regular food. Only Mage Food and Gems.
It was an addition only a few days ago due to them not really having a reasonably easy way to access food and drink for mana and hp regen, as such, you can reasonably assume the regen would be equivelant to that of similar level food/drink