We've owned one of the 1 hole "balls of death" for 7+ years and no problems.
I've read these reports where there was one incident that was attributed to
the ball, but it doesn't ring true.  Now the grapevine seems to have
increased the number of incidents.  Stop and think for a minute.  Whose
ferret hasn't burrowed deep into a pile of clothes or a plastic bag, nodded
off, and lived to romp again.  If they were going to suffocate, there is a
likely scenario.  Even if the ball were resting on the hole and the ferret
slept there, no air tight seal is formed.  These are burrowing creatures
that once lived in low air exchange tunnels.  Basically, I don't know how
much a part the ball played in the death and I certainly don't think whoever
it happened to did more than pick the likeliest target as the cause.  There
have been far more recent ferret deaths in dryers and dishwashers on the
FML.  But I don't hear anybody warning about getting rid of appliances of
death.
 
Anyway, we've exposed 9 ferrets to ours and 6 of them love it.  They play in
it all the time.  One of the big games is the 1st one in defending the hole
and preventing any other intruders.  Another common sport is 2 or more
inside and fighting, with the attempt to escape out the single hole leaving
that one open to attack.  Kind of like these wrestling cage matches with no
pay per view charge.  Because of the "death" tag, the maker redesigned the
ball with 6 holes.  The 6 hole ball would kill these games.   Never had need
to use our ferret defribbilator to resuscitate the near dead either.  We
have a whole code cart on stand by and practice CPR on our resci-ferret doll
just in case.
 
Charlene, these balls predate the fun tunnels by many years and are made
deep in the heart of Texas.  It may be form following function or copying
that they resemble your connecting nodes.  The nodes could have been cubes,
but spheres use less plastic (surface to volume ratio) to make and the
manufacturing may be easier.  Can't say for certain.  They may be equivalent
(I've not seen these nodes) in design, but they may or may not be the same
type of plastic or thickness, etc.  In short, they are not the same thing,
but may be so close that the result is the same.
 
   ( )--(a)
   (@=@=) \     Till next time.......Rudy the ferlosopher
   O__)  \ \___
      \   \
      /\ * )  \
[Posted in FML issue 1395]