Those designs are cool, but the problem I have is the cost of the Ego twist is the cost. That one is $35 for one battery that will go bad in a month or 2, and have to be thrown out. But even the solid colored ones are $25 apiece, just for the ability to adjust from 3.4 -4.7V or so. It would be cheaper to buy an 18650 Li Ion VV device that goes from 3v-6v, so you could just buy new batts for $11 when they go bad, and they have much better capacity and battery life!
I bought a Lava Tube/Torpedo VVV kit from Totally Wicked for $67, and it came with the variable voltage Torpdeo VVV(Lava Tube) with a charger and 2 Li Ion 2200mah batteries, a clearo and a nice case for it all. I've since seen them even cheaper than that. Thats the price for just 2 Ego Twist batteries.