Each time I have had SFU in my booking (or to be precise, each time I have known it was put there), I have not had any free upgrade. On the other hand, I have had several opups where (as far as I know) SFU was not noted in my booking.

(I should add that I have never asked for SFU to be put in my booking - each time has been entirely voluntary and unprompted on the part of check-in staff.)