After a week of use, this is my review: I think this is neither as stable and neither as heavy as people make it out to be.
My keyboard (a yamaha P125, which doesn't reach the back rubber pads, so I had to use the glue on rubber chips that came with the product to fix it) still rocks considerably back and forward, specially if I play at an angle. Maybe if your keyboard has a longer depth it won't rock as much, I don't know.
And I didn't find it all that heavy! Which is a pro in my opinion! PERFECTLY transportable to gigs, even more so because of the shoulder strap.
All in all, a great support but I was expecting no wooble whatsoever stability for a 150€ stand which didn't happen.
Also, this is IMPORTANT: K&M is the only brand that I'm aware of that makes stands that can go low enough to play your instrument comfortably, so just for that this is worth the price in my opinion. It goes as low as 60cm which is great, most stands go around 65cm.
Oh, and it's great that there isn't a metal bar between your knees and the keyboard. Other K&M stands go as low as 60cm but there's an extra steel beam to clamp your legs uncomfortably. This is just great in that regard.