In recent years, Routledge has gone from consistently producing excellent language courses to producing some excellent courses and some bad courses. Unfortunately, Colloquial Catalan is a prime example of the very worst Colloquial courses.
The main error in this course is the fact that it's exceptionally limited. After completing some of the other, more extensive Colloquial courses, you will master the grammar of the language and have a solid basic vocabulary. Colloquial courses like Colloquial Italian, Colloquial Czech, Colloquial Albanian or Colloquial Icelandic list over 2000 words. The average Colloquial courses list 1000-1500 words. In sharp contrast, Colloquial Catalan doesn't even reach 600 words! Hpoing to be able to communicate with such a limited vocabulary is fruitless.
Fortunately for the reader interested in learning Catalan, there are better courses available. In my opinion, the Colloquial courses are often a better option than Teach Yourself courses, but that's certainly not the case with Catalan. The old version of Teach Yourself Catalan is the best one, about three times as extensive as Colloquial Catalan both in vocabulary and in its explanations of grammar. The new Teach Yourself Catalan isn't as extensive, but it will still teach you more than twice as much as Colloquial Catalan.