It may be disgusting, but it is not gross like Fernet

http://www.tresagaves.com/products/margarita - I seem to recall this stuff was pretty good.

(1) Anything that has a fresh citrus component is usually icky icky eww when using an artificial substitute.

(2) Since the tequila taste comes through in a decent margarita, a decent tequila is important (not just for headache reduction). Top shelf not necessary, but steer clear of the bottom shelf, or anything that has phony gold color.