Well, I have fibromyalgia, a bad back, and arthritis in my hands, knees and hips as well as chronic tendonitis. The knee things don't help! What does help is moving around a lot. I also bought a few of those kneeling pads, the soft spongy ones, but I found a few which were twice the size of the older versions which were about 9 inches wide. I pile them on top of one another and kneel on them.
Actually, the only thing that works is when I'm finished gardening, I take a swim a hot tub and a nice cup of tea with a few darvons PRN!