I use this extension to "link" two x-stands and have an upper keyboard while playing standing. Varying the distance between the lower stands solves the problem of the limited adjustability that you may face if you play seated. Also, you can improve the stability by having the braces tilted to the side. In the upgright position, they swing quite a bit if you play heavy.
- Low price
- Stable, at least in my application
- Cheap build: one of the screws is scraping against its hole, even when loose and not mounted.
In conclusion, I would suggest giving it a try and see how it works on your setup. Worst case scenario,Thomann's aftersales service is always on point.
EDIT: After a couple of months of reharsing 3 days a week, one of the threaded holes has broken. I had to replace the tightening screw with a slightly bigger one, otherwise it would not clutch on the stand.