I saw the name squaresoft and got all excited about someone tying together a video game into filemaker.
( It's just Square. )
But yes, looks cool, and with USB attachments, could possibly be highly useful as a POS.
As for filemaker integration, square doesn't offer an API, so direct to/from connections aren't really possible. I believe Square supports the Square:// protocol scheme on iOS though, so you can possibly make a call from filemaker to open and pass info into square, just the return to FMGO would be an issue.