I think its cute, and considering mainly from a collector's perspective. Bracer looks too small to incorporate directly into am ACB costume. This looks maybe about the size of an AC2 bracer, and a to scale ACB bracer is considerably larger.
This is also not automatic, basic spring load, manual retract.
Poopa- you're better off DIYing it, someone on youtube broke down anumra's working one, replicated it using craft sticks and cereal boxes, and posted a tutorial. Kudo's to his reourcefulness!
Hidden Blade Dual Action Assasin's Creed (Tutorial) - YouTube