I have tried a bunch of these - BYJU'S, Vedantu and can’t recommend either.
But having said that, would like to add that good tools which teach children well cost money. While Khan is great and free, in practice, you would need to be quite a focused child to really stay engaged for long.
At
Flourish, which is our learner driven school (no teachers, young people teach themselves), we pay quite a bit for the tools that we use and can’t be happier. They are great, engaging and the outcomes we have seen justify the cost.
While some of our students do use Khan, most of them use stuff like Dreambox ($100 / year), Beast Academy ($12/mo), Lexia ($220/year), Spelling City (Rs 14k/class of 30), Primerry ($20/mo) and
DIY.org ($50/year). I am sure I am forgetting a couple.
Check these out. You will see what I mean. They are excellent and they add up. (These prices are per student BTW).
They have teams of excellent educators, game designers and engineers working on this. I can’t expect these to be free. While Khan is a noble initiative and makes great education accessible to the masses for free, that altruistic path is not an option for many companies.