Couple years ago I've stuck with the problem: usage of 2 keyboards simultaneously needs good solution. Standard "X"-styled stands are really not good. They can be really good for 1 keyboard, and even quite stable and comfortable. But them are not suitable really, if you use 2 (or more) keyboards at the same time. Different stands have their own problems (most of them were born in attempts to solve some other problems :) ). As result - these solutions are really not good enough (or at all - depends from specific model).
And, some time ago, when I look for Nightwish concert, I noticed quite interesting and unusual stand, which stays as rock, surviving the storm of emotions of Tuomas Holopainen. I starting to looking for this magic stand, found it in different groups, and finally, catch the frame with close-look for this stand, where I was able to read name - Spider. All other - just a technical question. And for now - I'm happy owner of Spider Pro.
It stands without any movements, when I perform, using my two keyboards (important note - one of my synthesizers has weight about 15.5 kg (!)), the only little problem, that arms, which hold keyboard slightly springy under during performance, but this is not a problem at all.
Another great feature of Spider Pro - this is a module system. I use Sheet Music Holder, which can be easily attached in a couple of seconds by one hand movement - very comfortable!
Height adjustment is another great function. You can fix "arms" for keyboards or any other additional modules at any suitable level without head-acke for changes in distance between arms, angle of "second floor" etc. You can just slide holders of Spider downward and use it at any needed height, so you can perform sitting or staying - without any problems or inconvenience.
When Spider Pro is folded - it just a compact pillar.
And last (for my review, not for Spider) greate thing - this stand takes much less place on stage, then other stands, and save for me possibility to use place under it for pedals or foot-switches.
The only thing - is quite big weight (about 10-11 kg), but this is reasonable price for incredible stability on stage!
Summing: Incredible, stable, compact, module, adjustable - this is the 5 words, which should appear in the mind, when you speak about K&M Spider Pro. Thanks to it's creators!