Beat me to those answers Terence.

MS Tags do cope better at much smaller sizes, but then the reading of QR Codes is improving. For instance, I have a 15mm sq QR on my business card containing all my contact info - 32*32, 4 alignment indicators - which is set in a warm dark grey rather than black (horrors!) and yet is read by at least half a dozen scanners with no issues.

The only real advantage MS Tags had was the analytics, but then that it available from a multitude of sources for QRs now, with both free and paid for accounts available. I think it's fairly obvious from the wording in Microsoft's Ts&Cs that they were planning to charge at some point in the future, at which point users would be tied in and feel they had to pay.