I just gotta ask. So are they cheaper, more capacity, more available, stronger or what?
If I am correct, other than the foot plate, they are exactly the same! Price, capacity construction & availablity!
I assume you ask this to figure out why does it matter if they are the same.
If you want an extra mag for a SD, buy an extra mag for a SD!
The reason for my curiousity would be that if I purchased a SD9, & the Sigma 9VE mags were the same,
I would then have 7 - 16 round mags for each!
Which will come in handy in my USPSA shooting!!