They're industrial tools re-purposed for combat, so actual utility compared to real weapons is limited.
They offer the same modifier as kicking, but aren't limited to damaging the legs of your opponent, which might have occasional value. The optional piercing rule would be their biggest advantage.
They might have more esoteric advantages in universe. As industrial tools they might be easier for questionable groups to obtain. There's also the coolness factor.
-2 to punch. Most people don't punch much anymore since Total Warfare made it more difficult. With the blade, the punch and kick now need the same numbers.
The retractable blade hits on the full body table normally. To resolve on the punch table imposes an additional +4 penalty, making it harder to hit than a punch.