NTFS for Mac (Paragon) is a file system plugin for Mac OS/X allowing access to Windows NTFS drives. I've got history with this product. The current version I'm using (v6.5.1) works very well. I can access my external NTFS drives and read and write to them.
The previous version I installed didn't work - in fact it messed with random files during file operations rendering them useless after copying. I'm very glad I did tests first. It didn't destroy the file allocation indexes, fortunately, but I immediately uninstalled the product and it took me months to get the courage to try again. I just used a gigabit local network and a windows laptop to copy files in the meantime.
Paragon support was responsive and offered a new version to try but I didn't try it immediately because if there's one product that must not fail, it is filesystem driver software!
Months later I downloaded their updated version and tried a few tentative tests and it worked fine for me. Since then I've used it for over six months and it's been good.
So my advice: buy it if you work with external NTFS drives. But test thoroughly first before using with your hardware. And if the data is REALLY important, use a gigabit network or NAS (network attached storage) device to bridge the Mac-PC divide.