I feel confident these holders will support any keyboard up to about 25 pounds (about 10 kg) with no reinforcement.
The hooks on the end arrived a little loose on mine. No problem - just use an Allen key (not provided) to tighten them. They thread into a plastic insert which expands when tightened, to stay in place in the aluminum extrusion. I strongly recommend buyers check to make sure they are not loose. Just try to pull them out as hard as you can. If they move, push them back in and tighten.
Also, double-check the underside of your keyboard. On my Akai AX-60, the bottom is sloped toward the keyboard at the front, and the hooks are not long enough to safely prevent the keyboard from sliding off if it is sloped toward the player. The hooks are about 4-5 cm in length, but a length of 6.5 cm is required for the AX60. I also own a couple of older Korg keyboards with a similar slope on the underside, but I haven't tried them - I expect to encounter similar problems. For such keyboards, you must either set them up to be level, or replace the hooks - you could use wood, or aluminum bar stock (1/4" x 3/4") as I did.
