It is vastly superior to Khan. Had my kids go through both, so can compare.
That said, on higher levels there's some cruft that trains mechanical skills, and that's on subjects that are needed only in the scope of the US system. For Europeans these should be optional, alas they are not and this adds a lot of tedium and hassle to an otherwise rather frictionless process.
That said, on higher levels there's some cruft that trains mechanical skills, and that's on subjects that are needed only in the scope of the US system. For Europeans these should be optional, alas they are not and this adds a lot of tedium and hassle to an otherwise rather frictionless process.