Less weight will turn under the car - less vibrations into the car IMO in case of imbalance.
I bought it not for saving 5kg. I just want to get good propshaft without vibrations. In my country is unreal to find original one, and my old one custom made with craped UJ. The price for used cardan from UK with shipping to Ukraine is the same with this perfomanced new one(with shipping form USA). Price with shipping was 600$.