This works great!
I have this installed above my K&M Omega keyboard table, and K&M 18811 extension, using the K&M 18824 tray. The extension is holding 2 drum machines above 2 keyboards. Fitting the tray means that the 18811 & 18822 should only be installed in one position (normally you can choose the width of the 18811 brackets to fit your keyboard) however that worked out great for my requirements.
When I looked at the Omega series and the 3rd level extension online, I was worried that it would be unstable - it looks very light . Now that I have it assembled, I am very happy - the build quality is excellent and everything is very solid when tightened in place. This it feels like this will last for a very long time.
The brackets can be adjusted to give some flexibility in height and position (forward and back). It is very stable with my keyboards and drum machines.
I am happy with this purchase