Booster Fuel has 2 types, and this page talks about the other type, Low-Grade Booster Fuel. Low-Grade gives a Temporary Speed Boost.
Low-Grade Booster has a duration of 19 seconds. If that timer hits 0, you'll lose that Speed Boost. If Thruster Fuel is already loaded into the thruster it will switch to it. If there is no fuel in the thruster, it will go dormant until another round of Thruster fuel, Low-Grade or High-Grade is loaded into the thruster.
Once again, the only disadvantage of Low-Grade Fuel is that Thruster Fuel lasts significantly longer than BOTH types of booster fuel.