top of the line vs product

top of the line and product both are nouns.

Word	Noun	Adjective	Verb	Adverb
top of the line	Yes	No	No	No
product	Yes	No	No	No

As nouns, product is a hypernym of top of the line; that is, product is a word with a broader meaning than top of the line:

Other hypernyms of top of the line include merchandise, ware.

top of the line (noun)	product (noun)
the best (most expensive) in a given line of merchandise	an artifact that has been created by someone or some process
	items for sale to the individual consumer
	a quantity obtained by multiplication
	the set of elements common to two or more sets
	a consequence of someone's efforts or of a particular set of circumstances
	a chemical substance formed as a result of a chemical reaction