Not sure where you get that. Worthington (I have 2) weighs 33 pounds empty, versus 38.7 for the Faber. Buoyancy characteristics are -2.5/-10 empty/full for the Worthington, and -7.26/-14.76 for the Faber. I have a buddy with a Faber and you can definitely notice a difference. With all that said, they are both good tanks, and either way it allows you to shed a bunch of lead.
I was going by the set of faber and the set of worthington tanks that are sitting in my garage.