TaalCompleet B1 is split into Deel 1 and Deel 2 because the full B1 level is too large for one book. Each deel covers roughly half of the B1 curriculum, so together they form a complete course. The split also lets learners pace themselves and choose where to start based on their current level.
In practice, Deel 1 usually introduces core B1 grammar and everyday topics, while Deel 2 extends into more complex language and skills. The two parts are designed to be used in sequence, but you can sometimes jump into Deel 2 if your foundation is strong. Since you scored around 90% on the free B1 instaptoets, you likely already have a solid base. That means Deel 1 might feel slow, especially if you have learned other languages before. The material is known for being thorough and supportive, but it can be less challenging for experienced learners.
To decide, look at the table of contents of both delen. Check whether Deel 1 covers grammar you already know well. If most topics are familiar, consider starting with Deel 2 or using Deel 1 only for quick review. You can also supplement with other resources that focus on speaking and writing at B1 and beyond. For example, conversation groups, online tutors, or Dutch Fluency style practice can add the challenge that a standard workbook might lack. Before buying, borrow both delen from the library if possible, or preview sample pages online. Try a few exercises from each to see if the level matches your skills. If you find Deel 1 too easy, you can always move faster or skip to Deel 2. The key is to use the split as a flexible tool, not a rigid path. Also consider your goal: if you want to pass the Staatsexamen NT2 Programma I or simply become more fluent, you may need extra materials beyond TaalCompleet. The series is a solid base, but it is not the only option. Weigh the cost, your learning style, and how much time you want to spend on review versus new material.