Am I worrying un-necessarily?
I was using the bath the other day and it occurred to me that if the moulded in nut in the centre of the bath waste failed (its been okay for 22 years) then I would wreck the ceiling of the lounge below.
Should I worry? Is there a better type of drain outlet fitting available? I did once replace a similar one on my kitchen sink when it broke when I tested the screw for tightness. however, bath wastes are a bit more difficult to access.