Hi,
Let's look at your question from a different perspective and focus on what is it that you are trying to address and what does the admission committee really look at.
Your GPA - In your case if the GPA is on the lower end and the admission committee(adcom) looks at education qualification to check if you will have the academic potential to go through the course.
A good GMAT Score would work fix that problem.
Taking courses of EdX is good - more to have a good understanding of what you want to get into eventually and show the adcom that you are interested in product management. When you talk about your post MBA career goals (if it's product management) and back it up with certifications like these, it will help.
These courses are not really going to fix your low GPA issue. If you are aiming for top 20 schools - improve your score by another 20 - 30 points would help.
Regards,
Shree