I have one that I bought a few years ago. Six months daily use in combination with physio and focused exercise made a noticeable difference to my posture I.e people actually commented that I was standing taller and straighter.
However, the brace was uncomfortable and I could only wear it for an hour or two at a time. I still pop it on occasionally to ‘remind’ myself what good posture should feel like. A quick google suggests there are better designs available that may be more comfortable than mine.
If you are serious, I’d consult a physio. It will take time and direction to get results. I wouldn’t recommend doing anything without a professional assessment/guidance.