I use this stand at home to hold Studiologic SL88 Studio MIDI controller (13.7kg), and recently added the optional 18811 second tier attachment to hold a Nord Electro 6D 73 (9.2kg).
As you'd expect from K&M, it's well made and very sturdy. I don't have any worries about leaving the keyboards on it; it's impossible for it to tip over, I'm sure it won't collapse, and it doesn't wobble in use. So, it does its job very well.
I only gave it 3/5 stars for handling because, while it's not difficult to dismantle and reassemble (remove two screws from the arms and undo two tool-less bolts to remove the legs), it's quite bulky even when disassembled. I wouldn't choose this stand if I wanted something portable. But, most portable stands are not as sturdy as this stand, so that's a compromise either way.
My only complaint is not about the stand itself, but rather about the 18811 second tier attachment: even at the minimum height, the second keyboard is higher than I would like. I didn't mind this when I bought it to use with a single keyboard (so I won't take any stars off for this), but if I'd realised I would want to add a second tier later, I would have gone with a different stand.