I'm happy to address your question about our change in recommended Math product for Grade 3 and above.
As with all of our curriculum packages, we regularly review the materials we include, keep in touch with products that are available to the homeschool market, and solicit and review feedback from Sonlight customers. Math-U-See is a product that comes highly recommended by our customer base, and our review of the program supports the significant positive input we have received.
In a nutshell, Math-U-See is a mastery-based, hands-on approach to teaching mathematical concepts. We find it to be compelling because it stresses both teaching concepts and the "why" behind them, as well as incorporating all the senses to help students retain what they learn.
We do still consider Teaching Textbooks, as well as the other Math programs we carry, to be excellent choices for your family. Please feel free to make use of the various assessment tools we've provided to help you determine which Math program is the best fit for your student(s).