From the designer, Devin Olsen:

Jigging and drifting streamers on a Euro nymphing leader is a deadly technique especially when standard nymphing approaches fail to produce well. Effective patterns for this method have mobile materials but also a slender profile underwater and extra weight to get them to depth quickly. My favorite pattern for this approach is the Backflop Jig which has just enough movement and flash to catch the attention of trout, but it also sinks quickly. It works well dead drifted as well as jigged during the drift with the rod tip.