Why? It's mechaniclaly centered by the spindle. And I don't think the
plastic pack casing would do much if the disk did decide to break up, so
not having the casing is not much of a hazard.
I would be more conserned with getting my long hair caught in the disk.
Just a few days ago I got a few hair strands nibbled of by the fan of an
RA90 disk :)
Judging from Philips other videos, this might be an issue for him as
well :)
/Pontus