database – Using UNIQUE (col1, col2) or using a composite primary key for a relationship table in SQLite / SQL?

I'm working on a project where I'm using SQLite and where I have a few tables of relationships similar to this one:

CREATE TABLE tag_entry_relation
tag_id INTEGER REFERENCES tag (id),
entry_id INTEGER REFERENCES entry (id)

I know that the two "reference" columns will be together together (so there will be no duplicates).

I am considering whether to use the UNIQUE constraint or if it is better to use a composite primary key

The reason I see to use a composite primary key is simply that it requires one column less than the other option

I do not see a reason to use a UNIQUE constraint, except that I'm more used to this than using a compound primary key, so I'm worried that something may be missing

What would you recommend? Grateful for the help!

PS: As far as I can tell, there is no difference between SQL and SQLite with respect to this question