I interpreted the use of the cube differently. When you consciously want to be in a particular mode, set up the cube. If you get interrupted, the cube is there to remind you what mode you were in. If you get sidetracked by "doing" 2-minute things and start to "do" a longer item, the cube is there to remind you that you're supposed to be processing.
I see it as a reminder. If you choose to continue to do the longer item, you can either leave the cube on "processing" to remind you to go back to processing when the item is complete, OR move the cube to "do" to make a complete mental shift away from processing.
There would also be the satisfaction when Processing is complete, to turn the cube to another face.
So far I've made two cubes without labelling them. One was made per the design, white on the outside with the extra set of cards to make it smooth. The other was made inside out with the flaps and the business card content showing, just because. Do you think they'll be more useful if I label them?