The Fujitsu ScanSnap S1500 is “made for” Windows, and the S1500M is “made for” Mac. What that really means is that they are different colors and ship with the appropriate version of Acrobat.
However, if you switch from Windows to Mac, you may not want to buy a new scanner. Easy enough; you just need the Mac version of ScanSnap Manager, and your S1500 (no M necessary) will work just fine. You don’t even need a copy of Acrobat, I suppose because a Mac has PDF support built-in.