The variable tube was not so much meant as a variable extension tube as a focussing mount for the 135 mm lens.
That's why it (like the bellows) starts at 63.5 mm (the amount needed to put the 135 mm lens at infinity focus).
The close-focus limit of the 135 mm lens on the variable tube, i.e. at 85 mm extension, is 1.15 m, field of view 36 cm square, scale 1:6.4. So not really very close.
The variable tube can of course be used with other lenses, but with the same drawback as the belows: minimum extension of 63.5 mm, plus the added drawback that the range of 21.5 mm does not do much (compare that to the range of the bellows: 138.5 mm.)