This upper back brace does not 'force' you into position. It gently pulls on your shoulders, constantly reminding you to keep your shoulders back and hold the position yourself. With repetition, long-term muscle memory is created, and the correct position can be achieved without conscious effort.
A back straightener that forces you into a position can weaken your muscles further and worsen your condition when you take it off. The brace is designed to help you hold your posture by yourself.