
Chocolate bitters are concentrated cocktail bitters flavored with cacao and aromatic botanicals, dashed in to season a drink — cocoa bitters are the same thing under another name.
Cocoa is what it is for, and a general aromatic bitters brings the bitterness without it. If the drink is built on the cocoa note, no other bottle carries it in dash strength.
Chocolate liqueur / crème de cacao
Sweet, lower-proof and poured in real measures rather than dashes. Two dashes of bitters become about a barspoon of liqueur, and the drink gains sugar and volume — take both back out of the build.
It separates and it settles, and both are normal — the cocoa particles are suspended rather than dissolved. Give the bottle a slow turn before use. Nothing about the flavor changes appreciably with age.