The build quality on the two heavier versions seem much better, much thicker chassis, thicker pcb, even the screws are bigger. I expect the two lightest versions are the latest, the question is, is this just a cost cutting exercise, or have the drives been improved somehow? To me, the lighter versions look much weaker with regards to durability, only time will tell.
Looking forward to hearing your thoughts on this, especially if you know what they have done and why.
Many thanks and Kind regards