Since you have to hit level 50 to get Specializations, the extra EXP armor mod doesn’t really seem that useful except using it as a way to get through Specializations quicker.
Since I will be getting LE, I will choose this Specialization first so that I can use it for the rest.
When you are progressing through a specialization, you will be using your custom loadouts in order to ultimately unlock the respective armor mod. Beforehand, you won’t have access to it. So on your way through Pioneer, you WON’T have access to Fast Track. But once you hit Lvl 10, you can add Fast Track to your custom loadouts, and use it for your NEXT specialization.