I have been using Reading Horizons in the Adult Reading Lab since 1996. It is a great component to the rest of the reading program.
The majority of my students are ESL students. They benefit greatly from the step-by-step approach Reading Horizons uses to introduce the students to the confusing rules of the English phonetic structures. The students also like the extensive practice provided in the Mastery, Drill, and Practice section of the program. The knowledge and practice they acquire while using the program makes them better, more confident readers, in my experience.
For the student who wants to improve their reading generally, the decoding skills taught in Reading Horizons are very valuable. These skills, combined with the large dictionary resource, makes Reading Horizons an important tool for any reading program.