>The author effectively wastes many words trying to prove a non-existent performance difference and then concludes "there is not much performance difference between the two types".

They then also show that there is in fact a significant performance difference when you need to migrate your schema to accodomate a change in length of strings being stored. Altering a table to a change a column from varchar(300) to varchar(200) needs to rewrite every single row, where as updating the constraint on a text column is essentially free, just a full table scan to ensure that the existing values satisfy your new constraints.

FTA:

>So, as you can see, the text type with CHECK constraint allows you to evolve the schema easily compared to character varying or varchar(n) when you have length checks.