The Eberlestock Batwing pouch is part of Eberlestock's proprietary EMOD system. The sytem of mostly-zippable packs, pouches, and accessories that are compatible with the F1 Mainframe.
By combining batwings with the F1 main frame and the Little Brother day pack you have a mid sized pack that can handle most any mission. Another possible combination is just the Mainframe and bat wings for a go in light come out heavy mission. This is great for those times when you have to hump that kill out of rigged terrain.
I think you get the picture, the Batwing pouches are one of the most popular parts of the EMOD system for a reason.
Get yours now, supplies are limited.