MOOC courses vary substantially in their quality. The ones on EdX, Coursera and FutureLearn, if provided by an established university or school, tend to be better structured and have better content than courses on places such as Udemy which are typically just taught by random individuals. This is not always true, but just something I've observed.
Most MOOC courses are not worth any university credits (or the equivalent for A-Level etc), regardless of who developed them. So the verified certificates are more like a certificate of participation and completion if you like. They don't hold much weight at all, but are useful to demonstrate hobbies or personal interests in an interview or sometimes on a CV if it is relevant. Some can be placed on linkedin profiles.
A handful of MOOC courses are actually worth university credits (or equivalent etc) and cost a considerable amount of money. If you complete these particular courses, you do actually get a proper qualification which should be equivalent to any qualification obtained by attending school or university. I don't know how employers actually view degree qualifications obtained in this way, but as I said, it should be the same. If in doubt regarding these particular courses worth university/A-Level units, check with the university or school.
A short word on "accredited". Some courses are listed as "accredited", meaning they are recognized by a professional body. In some of the MOOC courses that give actual university credits, the universities may call the degree accredited because it will also be accredited by a professional body. This may be important in certain industries like engineering.
However, some other courses which may not give any university credits may still be accredited by a professional body. You will have to look and read about the professional body to see whether the accreditation holds any weight in the industry.
In all cases it should be very clear whether you are obtaining an actual recognized qualification or you are just doing a basic certificate of completion and whether or not it is accredited. To sum up:
MOOC Course Type 1 - Not accredited and no university or school credits.
MOOC Course Type 2 - Not accredited but has university/ school credits.
MOOC Course Type 3 - Accredited and has university/ school credits
MOOC Course Type 4 - Accredited and no university or school credits.
Type 1 is the most common type of MOOC course.
Now moving onto the content, one problem with these courses that don't give any credits is that many lack detailed and plentiful examples and questions. They aren't really that much different from something like Khan academy. If you want to learn A-Level maths, there are plenty of free books available from openstax and others:
https://openstax.org/subjects/mathhttps://www.stitz-zeager.com/https://www.gutenberg.org/files/33283/33283-pdf.pdfI would strongly recommend reading books as opposed to watching videos. Books go into much more depth. You also spend more time learning the material so the chances are it will stick with you longer. At the very least, you will remember that you read the book and therefore if you go over the material, it should be simpler. Videos should be supplementary to learning. The only exception to this is watching full lecture series from universities or schools such as MIT openware which are made available on their websites or Youtube.
Note also that MOOC courses are different from professional certifications. You gain a professional certification from places such as Microsoft, Amazon, etc and these are typically found in IT for example, to demonstrate certain levels of experience. You have to study and then pay to sit an exam (pre-covid this would be in an exam hall in your local area). A professional certification is usually recognized in industry, provided it is from a well known establishment.