Kite--I hadn't seen that before, no. But most of us here are shipping in winter temperatures that are in the 30s or higher. The problem I ran into here is that when you drop the box off, it may be held for hours in a facility at normal room temperatures. This is potentially fatal.

72 hour heat packs do not supposedly exceed 110 F, which is the same temp achieved by 40 hour heat packs, so it shouldn't really make a big difference.

I prefer 72 hour because shipping delays can happen.