This reappears every so often. About 6 mos. ago I was taken aback with the same thought. So, I weighed my new purchase. The bulk of the weight is in the chassis cabinet which as stated is standard to take combinations of trays. I unscientifically, inserted what is presumably the median weight, e.g. equal portions of small medium and large trays, 3, 3, and 3 or whatever it is.
It weighed 11 pounds empty. But, gosh, is it solid and the secure trays - firmly lock in and so forth is sure superior.
Also, rarely mentioned, the tops of the systainers make good small work surfaces for miscellaneous parts in progress, assembly, etc. without rolling off or all over a cluttered workbench - not that anyone here has cluttered benches.