This is somewhat same like Alison.
They privides lacs of free courses but you need to pay for the certificate. Te cost of the certificate is bit expensive. But it is worth. Because it is coming from great universities like havard ect.
But if you dot want to buy certificate you can enroll a free course.
Compare to alison it provides more documents( theoritical) part.
And the instructors are from Universities like Havard, MIT ect.
And you can also attact your score on your resume.
So dint think just sart your course as earliest. You are at the right place.