After having read several horror stories about drives partitioned for both the Mac and PC file systems - in which the user usually lost data on the Mac side while the drive was being used with a PC - I've come to the conclusion that if you have Mac-created data that you _value_, don't entrust it to a "dual-formatted" drive.
Instead, keep it on a Mac-ONLY formatted drive (either partitioned or not).
If one needs a "dual-formatted" external drive platform, get a SECOND drive for that.
Put PC-formatted data on it, and Mac data if you need to, but again - put the IMPORTANT Mac data on the Mac-only format drive.