I used MUS from Alpha to Zeta and always supplemented. Not because it was lacking, only because I knew due to the mastery approach the kids may not have learned a skill that would be on the state standardized testing, and I didn't want them to think they were behind. I went through Abeka, BJU, & Horizons as supplements before I found CLE, which I generally used one grade level lower, and for us they were the perfect combination.