But this could happened only if the SB is before all of the other tasks, because the SB is an obligatory task - only the last team in a NEL must complete it -, you can't skip it. And we saw B/M at the SpeedBump with the mark in the forehead. Following your reasoning they avoid also the SB so... why are they at the SB location? And what's the gain of taking the FF (or, at least triyng it) if you've got to stop later to do the SB, giving the other teams the chance to make up time?
Simple, a FAST FORWARD usually gains its winners one to three hours versus the other teams (although it is sometimes more as in Amazing Race 5 in the Cairo area and sometimes nothing as in Amazing Race 10 for the Madagascar cow lips). That might conceivably make up enough time for Mark and Bopper to stay in this race, although I don't think so.
It's a matter of time, as I've been saying since the beginning, and you are too in that post: time is the key factor in this leg (by the way, Colin & Christie took a hughe advantage in Cairo not only for the FF, they flyed to Egypt earlier than the rest of the pack, arriving by night meanwhile the others had to stay at the Frankfurt airport waiting for the next morning flights; I know you know that but is good to remind it; and you're right about Madagascar - something that let us a moral, never take a FF when you're Intersected and you must eat cow lips
But seriously, what I'm trying to explain about the whole FF/SB/DET/RB and the forehead red mark is just like in the next season the race start in Usa, and the first leg is in Japan, and the 2nd. in Brazil, and the 3rd. in China. It has not sense that the bindi was at the end of the Detours and then teams get the instructions for the FF, as someone stated (would you consider - as a member of a team - to try the FF with only the RB between the PS and you?). The spirit of the FF is to allow one team (two if they're Intersected) skip all the tasks of the leg and gain the advantage you mentioned, and this is the reason they're always at the first route marker. What leaves us with two possibilities:
a) the bindi is a part of the FF (your very plausible theory) or b) it comes with the first route marker (as I believe) in some sorte of ceremony (I've got a flashback of a leg in Southeast Asia when, in order to receive their clue, teams must participate of something similar; only I can remember if it was in TAR or TARA or TARAUS).