I was shown the fuel flow technique on my first IOE trip, surprisingly it worked and you were nearly dead nuts at 300kts at 1500pph/e. It does get you in the right ballpark for fine tuning speed in cruise and descent.

I found most of the older captains who have flown 5+ types with my airline would use this technique since it worked so well on the older steam gauge aircraft. On the flip-side, all of the instructor pilots I have talked to or flown with agree that if Bombardier wanted you to fly the plane by FF then they would have made the numbers bigger on ED1.

I was told that a new pilot was taught the FF method on IOE and used it all through the first year. During their PC the FF gauge was inop on the sim and since they didn't know how to fly any other way, they failed the PC.