It will absolutely fit as a replacement for the F/F coupler. I just installed one myself, although internally in the seat tube, but I put it in place of that very coupler up front to update the firmware and get set it up since doing so requires disconnecting and reconnecting it. I also didn't use the app; the BCR2 charger/programmer and E-Tube Project on a Windows computer can update the firmware and it's a whole lot more reliable than some BT app.