Pros and Cons of having additional columns in join table of many to many relationship
In general, the wider the table the slower the query. But slower doesn't necessarily mean slow.

The number of joins probably has more to do with the use of id numbers than anything else. Natural keys can speed performance dramatically when the important information is carried in the key. (This happens more often than you might think.)

The M:N table is the natural and sensible place to store information about that M:N relationship.  So adding columns to store information about that relationship makes perfectly good sense. Wider tables are usually slower, but narrow tables that don't store data are less useful.