How I Use It
I use it to let students work at their own pace. It gives me the opportunity to work with students that are having problems while letting those students who are comfortable with the material to move on ahead. Some students lose focus while working with Learnzillion. It shouldn't be used for too many consecutive class periods. The pretests are good to give before starting a new topic to get a feel for where students are at. A downside is that the pretests are not very extensive and are only in multiple choice format.
I would recommend it as a teaching tool, but be wary of using it too much as students may lose interest.