This topic has been written about at least 1000 times. But hardly anyone seems to have highlighted the biggest practical difference between Open Source and Shared Source: That you can modify Open Source software to fit your device (and other software), while Shared Source only lets you modify your device (and other software) to fit the Shared Source software.
You are eligible for Microsoft's OEM Source Licensing Program, so you sign up for it. And Lo! One of your very smart employees soon figures out a one-line change to Windows that stops the UnSupers from crashing. Then you remember Microsoft's Shared Source licensing terms, among which is this fatal clause:
Licensees may read and reference the source code but may not modify it.