It's a really cool system actually. You form the shape with some sort of wire mesh, we used 10cm x 10cm fence leftovers. Then you line the structure with straw, and layer in potatoes and soil. We used peat moss and what's called black soil around here, leaving about 10-15 cm between the layers, with 4-5 potatoes in each layer. The towers look really pretty before they start growing, like round hay bales, and after that you just have a sort of potato bush. Chickens seem to like the leaves though, so I'm a bit worried about how the bottom parts will look.
The tomatoes seem to be going nicely too, we've got two cherry tomato varieties. The tall ones are about 4 feet high, and counting the fruit that's growing and all the flowers, both are producing about 150-200 cherry tomatoes if all goes well. The totem plants are about a foot and a half, and each of the four we have are hopefully going to make about 50-100 cherry tomatoes. That should be enough for us, I might even make some canned marinara sauce out of some of them.