As a proponent of DUO 3.0, I feel example sentences are a little bit boring and inefficient. Another dissatisfaction is accompanying CDs don't include the sound of example sentences. At the expense of such limitation, this book provides a good deal of vocabularies.
By the way, I've read an intersting ariticle that compares the numbers of vocabularies needed for various tests and media.
The author maintains many English words that are taught in Japan are less frequent and unpractical. I don't know whether it is a generally applicable argument, but personally I agree with that. Although I can understand essays appearing in the grade 1 of Eiken, I know I still lack many basic vocabularies.