The basic point of those chairs is to force an active, upright and changing sitting position that will keep the couch-potato posture at bay for another few years. I see Lone is already pretty deep in his seat at a tender young age (another thread). While the chairs have knee support, the key is that they allow for variety. You can sit with both knees on the supports, alternate knees on a support with the other leg stretched in front of you, or just normally like you would at the local bar (at the start of happy hour). I do agree that prolonged pressure on your knees in a kneeling position is the equivalent of penitente. But the chairs can be quite subtle. Even with both knees on the pads, slight adjustments in the balance of your torso will quite radically change the amount of pressure. More weight back, sitting with the center og gravity running down your spine, will leave your legs folded but intact, even after hours of sitting. I can’t stress enough how variety, not the one solution or ultimate chair, is the key to keep strain and possibly injury at bay over time. Sometimes I pull up a regular office chair and use it for a day or two to gain another posture. A cheap exercise ball from the sports shop can be a great way of doing the same.