I have used this resource at both the beginning and intermediate levels. Students are immediately drawn into the humorous, but very efficient presentation of the grammar points. In classes where a natural language approach is used, students frequently seek a concise, English language resource outside of class. Tex's grammar fulfills that need.
The site is extremely straightforward and has a clear navigational scheme. The credits page shows that a large design team had input on this project. The site index and search features are very useful.