This posture corrector is great to help you train your posture a little bit each day. I got the XXL, but I could have easily gotten the XL, since the straps are so adjustable. It is very gentle support, this is great for temporary support, but I've seen people saying they got it as a back brace, and it definitely will not work for that. It should only be used for a short duration each day to help train your muscles back into the correct shape.
I do think the Velcro-like parts could be a little stronger, having small straps with Velcro on them can make it hard for them to stay in place unless your really press the Velcro down and smooth it out.
The sewing is very good, and the fabric is very strong. I would not plan to use this under your clothes, as it is bulky, and the fabric will trap sweat against your skin.
This posture corrector is great for the price, and I'm happy with it overall.