I saw one on aliexpress for $4 and I'm wondering if this would be a cheap way to prevent or reverse back injury over time stemming from sitting at a computer.
I asked my physiotherapist this question, the answer was "no", better to do exercises to strengthen your shoulder/back muscles. Start with low-impact exercises if you're not used to it yet.
I've heard mixed reviews. The core of the issue is that it doesn't help you strengthen weak muscles. Better to put some kinesio tape on your back to remind you to correct your bad posture.
How does kinesio tape help with weak muscles? Just correcting your posture occasionally won't do any good in the long run, either. This might "pull you into place" but no muscular strength is gained. If someone picks up a good routine to strengthen their weak spots, an improved posture will appear soon enough.
Sorry should have clarified. Some people use kinesio tape to remind them when their posture has sagged forward. It doesn't really help with strengthening anything but this is as opposed to posture corrector things that just forces your body into place. As you mentioned, strength training is the main requirement to fixing the core issue.