I don't see any issue whatsoever with the same stats being used for brass knuckles (in fact, I've been using Hardliner stats for knuckle-dusters since Cannon Companion came out).
Power fists and chainfists, though? Those are a bit beyond the tech-level of Shadowrun, at this point. Remember a power fist is wrapped in a disruptor field and is powered by strength-enhancing servomotors and is still a pretty fantastic, powerful, and rare piece of wargear in the 41st Millennium...and that chainfists are everything power fists are, traditionally, but better. I'd say both of them are well beyond the reach of 2073.