I am in full agreement with David Crane, who says that the VBR-B Compact is “arguably the most intelligently-developed PDW weapon/ammo concept to date“. Why? It is small, can fire 9x19mm armor piercing ammunition, uses glock magazines, includes a foregrip and is not much bigger than a Desert Eagle pistol.
I highly recommend the detailed article David wrote about is at Defense Review.
UPDATE: PersonalDefenseWeapons.com also has info about the gun.