Have sold 300 of these XA/XB kits at this point...with lots of positive feedback and no complaints. They especially help with taming horizontal movement...the thing I see as the biggest weakness in the 50-60 year old originals. Lack of lateral movement will aid in better speed stability because the belt will no longer pull the whole subchassis towards the motor.
As Christopher P notes, this is NOT the ES-1/EB-101/AR the TT kit, which is a stiffer spring, requiring the addition of mass or a record weight if used on the XA/XB.
Dave