They are really nice. However, they are harder than the real TOEFL. If you can do good in this material, you will be reach a high score in the real exam.
Other point, they just have two voices and they are professors. The TOEFL has professional voices, they are clear and use to understand. Moreover, the TOEFL questions also provide more detail and easy topics.
I have the official guide. Then, i compare both materials. For example, the question number four ( in the material above), example 9. If you can answer this question clearly you will reach high score (28 to 30) in the speaking section. In the official guide, you can see that question number is not hard at all. Thereby, you do not need dismay if you can not give a EXCELLENT answer in this material.
Gmat Prep: 540(45Q,20V) 5/25/2011
Knewton Diag 490(38Q,22V) 5/28/2011
Knewton 2: 520(32Q;30V) 6/16/2011