I thought pumps were constant velocity to maintain the pressure required by the injectors. If the pump slows down then when the injectors open less fuel will flow through them which the O2 sensor says is "lean" so it holds the injectors open longer OR increases pump speed/pressure OR the built in regulator closes.

I thought the FiTech incorporated the regulator in the TB.

Anyhow, I'd probably go with what the manufacturer suggests - it increases the likelyhood of the unit working properly!