With the hollow, adjustable design of the Hotchkis unit, it won't weigh much more than the stock link plates. With a solid bar the weight would be more pronounced, but the benefit of the bar would probably feel better and be more noticeable than the addition in weight.
Performance wise, not a big difference. Typically, axle hung bars are higher in gross force than the stock style bars, but the differences in attachement methods brings the applied wheel rates very close to each other