I just read about the FastFormat C++ i/o formatting library, and it seems too good to be true: Faster even than printf, typesafe, and with what I consider a pleasing interface:

  // prints: "This formats the remaining arguments based on their order - in this case we put 1 before zero, followed by 1 again"
  fastformat::fmt(std::cout, "This formats the remaining arguments based on their order - in this case we put {1} before {0}, followed by {1} again", "zero", 1);

  // prints: "This writes each argument in the order, so first zero followed by 1"
  fastformat::write(std::cout, "This writes each argument in the order, so first ", "zero", " followed by ", 1);

This looks almost too good to be true. Is there a catch? Have you had good, bad or indifferent experiences with it?

CW on this question, as there's probably no right answer...