"This sword is heavier than that one."
Translation:'etlhvam 'ugh law' 'etlhvetlh 'ugh puS.
vetlh as a word of its own mean "cockroach", so 'etlhvam 'ugh law' vetlh 'ugh puS is "This sword is heaver than a cockroach."
The suffix -vetlh "that" is only a suffix -- it has to come at the end of a noun and cannot stand alone. It's not a pronoun.
If you want a standalone "that", then sometimes Dochvetlh "that thing" can work.
Here, though, where "that one" refers to a specific object (a sword), 'etlhvetlh is best.