My sister reckons that the supplements help hers. She has stopped and started them few times and says that she can tell the difference. It could just be the placebo effect, of course.
I take Glucosamine sulphate (I can't afford the more expensive stuff) and have been doing so for over 10 years. My dodgy hips have not got dodgier at the rate I expected so perhaps the supplements are working for me? TBH, I don't want to stop them for 6 months to find out!
I had my sore hips x-rayed about 15 years ago and the signs of arthritis were already there. My dad's hips both packed up before he was 60 and I was keen not to suffer the same fate.