A fluent site to help and engage everyone
I think it's great overall. I have told kids to get fond with that site more than the classics of sparknotes, etc. It offers all fields in math, science, english, social studies, gives great summary and analysis that every kid can understand, has tests and quizzes to support, and a ton of other things. Some teachers may dislike the occasional crude or risque comments or jokes, but I teach seniors, so it's generally pretty informal and they can handle a wide range of topics.
How I Use It
I have used this site for my own research, for students for support and study help, and lessons with engagement. On my own, it has allowed me to research stories and get quick refreshers with analysis for novels and poems in the English classroom (regardless of popular opinion, English teachers don't memorize every chapter in every book, so sometimes we have to refresh what was happening in chapter 25 of To Kill a Mockingbird). It has also helped just doing research into historical topics and their influence in a story, time period, etc. Students love it when I show the short summary/analysis videos, but be forewarned that sometimes they may make a few risque jokes, so trust and know your student body and watch it before showing.