I really like how the math manipulatives are large and the navigation is easy to use. One tool that this site has, that I haven’t seen on other sites is the balance scale – great for teaching equivalence. The probability and base ten blocks tools on this site are excellent as well!
ST works incredibly well when student have autonomy over their own learning. It can be difficult not to help students when they are struggling through a concept, but assisting them only takes away the power of the productive struggle.