I did an online undergraduate course on Philosophy through Oxford and it was really insightful - I definitely recommend doing it. You don't get a certificate at the end (well I didn't) but only a feedback form.
The feedback form stated whether you passed or failed, the professor's comments on your assignment and how your attitude to learning throughout the course length.
Yep you get CATS point at the end. For me, it was 10 points for the course and 10 points if I successfully completed by assignments to at least satisfactory.
I've been told that it is very useful to state that we did the course when applying to university since it shows that we love to learn - that we have broad interests that could be outside of what we want to do in university.
I'm applying for uni this year.