Yeah, it's significantly (22 pounds) lighter than its lead acid counterpart, but the trustworthy car geeks at Jalopnik insist there's no way this thing is worth the $1,700 upgrade price. The phrase "overpaid, insecure idiots" came into play. [Jalopnik]
It reduces weight, yes, which is gold on a racetrack. 22 lbs lost on a race car is like a lottery win. But it's also shorter, so the weight it does have, is lower in the car, thereby helping to lower the overall C/G - which is also racetrack gold.
Of course, most of the buyers will be balding insecure idiots who buy it for their appendage replacement vehicle because it's $1,700, not because they race their cars.