Has anyone else actually *used* mutation testing at all?

Heard a lot about it recently - it seems all the rage amongst the bloggers, but I'm generally always very sceptical of things touted as the "latest hotness" (my thoughts on blockchain for instance are well known.)

So I went ahead and whacked http://pitest.org/ into one of my more recent pet projects to see if it offered anything decent. Surprisingly, it did - in particular it caught a number of places where switching "<" for "<=" and similar had no affect on the pass / fail rate (indicating the tests should be better.) There were a *few* false positives, and some which were borderline useful, but as a whole I'd say it was a worthwhile addition.

Curious as to if anyone else has had the same experience?