2018 had worn them the last 4 years. As a Sports PT by trade, and after researching and reading, I liked the idea of them as he was growing. Being a pretty decent catcher, he was used to catch probably more than he should have been. No issues with knee pain, just soreness after catching back to back. We handled it.
He decided to stop using them this year, as he felt he could move better without them, and he noticed most MLB guys do not use them. I am fine with his decision. From a Sports PT aspect, the knees take a beaten due to issues above the knees in the spine/hip/pelvis, as well as issues below the knee in the ankle/foot. He will get regular, on-going assessment of all those areas, as he moves forward, as Dad can make that happen for him. That assessment and treatment (if/when needed) will not happen for the majority of catchers out there, so our situation is a little different. We are blessed that I am able to do that for him.
Our case is not a fair test, due to the sports medicine background, and our ability to manage the underlying causes of knee pain. I don't think the knee savers are firm enough, or positioned in a way to change the knee mechanics dramatically, if at all. I know they did not make him lazy or affect his ability to catch, block, or throw down. During a tournament, they gave his knees a break. All good things for a growing kid with soft growing bones.
I say wear them if you think they help, and they don't get in your way. If worn properly and kid gets good coaching, they aren't a problem. They can get in the way in certain situations, but otherwise no big deal.