Hi Kate,
I’m in a similar condition as you. Fused in 1974 from T3-L4 with one long Harrington distraction rod in the “Dollar sign” position running the length of a double curve and a compression rod on the convex side of the thoracic curve.

I haven’t used that brace you mention but my opinion is that anything that helps you find a “neutral” position for your lower back would reduce your pain. Soft cervical collars do that for neck pain and help the nerves and soft tissues heal. The wrist splints I wear at night stop the pain from synovial cysts and thickening ligaments causing nerve compression of carpal nerves.

How is your overall bone and muscle strength? Are you taking any hormone therapy to help improve bone, muscle and skin tone? I do dozens of small measures daily to help manage the consequences from an aging, extremely long fusion. These include daily walking, stretching that gently lengthens the muscles in my back, ligament stretches in my hips, nutritional supplements, Ca, D, melatonin, C to name a few. I focus on maintaining straight posture while sitting, driving, walking. I have extra mirrors in my house to help me check my posture. A thoughtful eating plan limiting calories to 1200-1600 daily for weight loss and maintaining at 1700-1800, based on NIH low cholesterol weight loss guidelines. I also aim for 50 grams of protein each day for long term energy and to keep from getting hungry.

I agree the risk from salvage surgery to correct flat back or eliminate back pain, which requires various vertebral osteotomies is extremely dangerous. There is no published data on the surgical outcomes, success or failure rates. The small number of known cases spoken of anecdotally by patients and surgeons indicates an enormous rate of patients made worse, or very temporary improvements followed by repeated surgeries with bad results. It is an exercise in futility.