I've tried several keyboard benches now, all of which had some issue or another and the build quality of each was disastrious. But the On-Stage KT7800+ is finally a bench that feels like it's worth the money.
Different to every other X-shaped bench I've seen, you change the height not by directly adjusting the legs with a pin or screw in the middle, but through retractable pins on the bottom of the cushion.
This not only makes it extremely solid without any wobble, but aligning it is much less of a hassle. It's a simple thing, but it genuinly is like a spark of innovation in a field that hasn't seen light in decades.
The mechanism aside, the legs are also thicker than usual and nothing bends or moves when you sit on it. I'm far from the weight maximum of 150kg, but I wouldn't be surprised if it could hold even more than that, if anything the cushion will give in first.
On that note, if I had to give one negative, it's probably the cushion. I'd personally prefer some kind of fabric cover over the faux leather, like the K&M 14066 has for example, as I find those more comfortable to play on, but it does provide solid seating nontheless.
It is much thicker and more firm than most I've seen so far, so it does feel higher quality than other faux leather cushions I have used in the past at least.
Overall I'm very happy with this bench and hope the cushion will last, as I have no doubt the base will.