When you export FBX to UE4
Does the exporter apply rotation and scale? Is root motion possible?
What kind of drawbacks are we looking at here?
I have not had any trouble with fbx from blender. You may have to orientate and scale it in blender first so when you import it into ue it is upright
once you understand how to set up the exporter options it’s ok , it’s always best to apply scale + rotation before you export
root motion should be posible though i’ve had no need to try
the main draw backs are very limited support (blender team) and can cause a lot of hassle if not set correctly
btw i have a few use full video’s on my channel for blender to UE4 
Aah nice videos dude 
It’s good enough for me.