David,

You've spelled Finbarr's name correctly (but not Willy Clancy's!)

Finbarr is a great collector of songs and I'd say his version would be as authentic as anyone elses. Variants of many traditional and folk songs exist and this looks like a perfectly good one to me. As far as I know Franke Harte, who's version would have been the source for many of the other recordings mentioned here, including May Black's, sing "The truth to you I mention", but I think the "Devil's own invention" is every bit as good (if not even a better) line in this context.