I have four of these stacked together. They add a lovely brightness to an otherwise dark shelf and I have no worries about stability. Each has about half a ream of paper on it.
Helped take my desk-mess to an organized project production line. I find current projects on my desk in a moment. Very helpful while on phone calls looking for my data.
I recently purchased the 6-pack of these trays to help my husband organize all the piles of paper on the table he uses as his desk. By being able to put each pile in a separate letter tray all of his papers are handy and easily found. It has given him more room to work and looks so much neater. We chose to do 2 stacks of 3 letter trays each as that works best. The boxes stack on top of each other easily and seem to be pretty stable. Purchasing the trays as a 6-pack is a cost-saver. I highly recommend them.