Originally Posted by Mad Cook
Charlie is correct.
A zester only takes little shreds of the very outside of the peel for flavour, decoration etc. This actually peels the fruit taking some of the pith with it.
I'm aware of that ( I have one), but it's only designed to take the sweet zest from the surface of the peel, not the bitter pith.
A peeler should cut all the way down to the pulp (and most peelers have a longer straight blade like a potato peeler). I suppose that this tool would take most of the peel off a thin skinned fruit like a tangerine, but not from a typical orange or lemon.