I have a pair and I love them! I don’t know if they help with any leg pain since I don’t have any but they’re definitely a lot more comfortable than normal stirrups, even freejump. I think they’re worth the money even if you don’t buy them to specifically help with any pain because you can definitely feel a positive difference between flex-on and normal stirrups
My friend has these and she loves them. I have ridden her horse in her stirrups a few times and I feel that they are comfortable. They give you ankle or foot more possibility to move around so if your ankle hurts in one position you can just move it. My experience and my friends experience are very good!