It was still an amex branded product. MS plat is nice to run through after regular plat 100k and MB 50k.
No, AMEX was the processing company.
The Benz Pt requires $3K spend for 50,000 MR's, and I don't believe it offers a free AU. MS is $1K spend for 50,000 MR's, and definitely offers a free AU. Unless you're in the market for a new Benz, the MS Pt seems like a better deal.