I like the adjustability Simon, both for when moving home and furniture, and also for experimenting.
My tweeter only covers the top octave, so adjustment allows tailoring for hearing loss, and also for the liveness of the room and reflections. Agreed, you can do without them if I live in the same place and keep the same furniture for the life of the speaker. But it does make sense. My hearing in the top octave will be considerably different yo yours for instance.
I haven't found the existing ones too harmful sonically - except for Bottleneck playing with them and making me think my system was a bit bright for weeks! All sorted now though. I've found some pads at Parts Express and might also be able to get some direct from JBL in France.
Thanks for the link though.