Anyway by the time my children have finished Horizons 3rd grade math they either start Saxon 54 or 65. Mostly they have been ready for 65. I have done this now with 4 of my children. No more clean math pages, like Horizons, now they have lots of geography thrown in which I find is confusing to younger children. It is hard in first grade to read word problems about Miguel in Guatamala and still catch the math concept.
Horizons has a cleaner look.
I don't use the teacher's manual anymore though because it is too time consuming. Just the math pages and some flash cards. The children have gone on to Saxon 65 without skipping a beat. I found it to be a very user-friendly curriculum, especially for a teaching novice like myself. It is very thorough and academically rigorous, particularly in the upper grades.