To actually make them heavier than the original Sortainers, they'd need to be made out of some sort of super dense black hole material [eek] [blink]
Even if they are slightly heavier, the effective storage density is significantly higher due to the new design.
If you can cash out of your old Sortainers I think it's a no brainer!
Quick hint .. Amazon shows the shipping weight for most things, but it's not going to be 100% accurate and will generally be greater due to packaging, etc.