I really like these a lot. hexagonal end-caps have been discussed before, and I am very happy someone is now actually producing these. I had previously thought that I would have wanted to build a pack out of all sections that held two cells (with the last row using single-cell pieces), but I think its possible to build just about any series and paralleled combination with 3-cell and 2-cell pieces (I'm assuming the multi-cell pieces are slightly cheaper when purchased in bulk).
I don't want to start an argument over pack-building methods and configurations, but I have stated many times in the past that I prefer the honeycomb layout over "rank and file". For those who like honeycomb, a few are still building by hot-gluing cells together. The cells should not touch each other, even with the stock PVC heat shrink on them. Not only for electrical isolation, but also for heat dissipation. Even if your pack barely gets warm in the center, the heat needs to get out if you want the pack to last.
If the cells on the outer edges of the pack stay relatively cool, but the handful of cells at the center of the pack are always warm, lets just imagine that the outer cells would retain over 80% of their rated capacity for six years, but the inner cells go below 80% after three years. Would you rebuild the pack by replacing only the inner cells with new ones? Of course not. The entire pack will only last as long as the handful of cells that are abused the hardest.
Tesla uses honeycomb and does not have shrink wrap on their cylindrical cells for heat dissipation. I think the fiber insulation-washer added to every positive end is a vital component, but after that, this is the pack-building system I would use.