If you want to get the best of your transport, try this.

@nonoise 

Interesting alternatives but.....
If only one half of the bearing is semi captive what is to stop whatever piece of equipment that is sitting on top of the bare bearings committing the audio equivalent of a Wal-Mart shopping trolley esque suicide?

I can just picture pushing a button on a CD player and the whole goes flying backwards skidding of the bearings!

Or am I missing something here?

@uberwaltz,
The site has been updated since I last viewed it and it used to have a top half captive piece as well. I'm assuming it was found to be not necessary or that what you imagine wouldn't happen.

If you think about it, you'd have to push really hard to move the unit and the bearing up and over the lip of the bottom piece, with force many times more than necessary. Anyway, I think you can still order more base pieces to use for the other half.

All the best,
Nonoise

Actually no, or at least I don't think so.
What I envisage is say the CD player just gliding along on the bearings until it slides off. The bearings do not move anywhere, just rotate in the bottom housing allowing whatever is on top to move easily and readily!

It is now just a variation on what we use to move heavy equipment around in factories.

I am a more confused as to how they can work without a top piece?

Well, they are cup shaped. It could be that the photos don’t depict how deep the cups are. They are convex. And as I mentioned, the older site showed top halves that matched the bottom halves with the ball bearing in between. If you are concerned about it rolling up, over and out of the cup’s lip, then you could ask for a top halve to ease your worries.

All the best,
Nonoise

Nope
Not worried at all about the bearing rolling out of the cup, think you may be missing my point.
With say all 3 bearings freely spinning in the bottom cup bases, anything placed on top WILL slide on those bearings very easily.
At least that is my take on it from an engineering point of view.