> I am guessing this add-on bit will require occasional adjustment, and/or loctite.
In theory, no.
The nut which clamps all this together is done up tight against the end of the leg pivot. This means the nut should never loosen, despite the legs spinning wildly. There are low-friction brass shim washers to cut the friction and prevent galling, so there is negligible torque on the nut anyhow. The stainless steel grub screw which holds the nut is jammed in place rather tightly - it does its own thread forming in fact.
> the brass nut locking the FM-300T burner on.
Yes, I wondered about this too. But the weight of the nut is actually very low, and it serves TWO purposes. First of all it locks the burner onto the stove body so it does not accidentally unscrew and fall off. In addition, it allows me to align the pot supports on the burner with the heat exchanger coming up from the stove body. In theory I could adjust the start angle of the thread to do this by itself, but if they change the start angle on the burner column with respect to the pot supports during manufacture I would be in trouble. In practice, I don't think that angle is even controlled during manufacture.
The change in position of the air holes with respect to the face of the jet would be at the most slightly under 0.2 mm for the worst case alignment. The distance between the air holes and the jet is around 7 mm. Methinks I will not worry.