I've never done waist training per se, but I do love a good corset.
My 2 cents - if it's $30, it's not going to do anything.
I've bought cheapish corsets - Frederick's of Hollywood type, and while they look okay, they don't have much structure. They usually have nylon bones, a thinner fabric shell, thin laces, and the closure isn't much beefier than bra clasps. You can get a little squeeze, but any more than that and things start failing.
I've also bought better corsets - $100ish, the "4 to 5 inch reduction" from Corset Story. It's made of heavy cotton fabric, has more boning, and they're steel, and the busk closure is heavy duty metal. The lacing is also much heavier cording. I can put it on and easily get my shape from a 41-40-40 to a 42-34-42. I haven't worn it long term, but I suspect that if I did, I'd get some "waist training" effect. That thing is sturdy, and in a fight between it and my body, I suspect it'd win.
I've also gone with the heavy duty elastic shaper. The heavy fabric does a decent job of holding me in place and giving me a figure, but it's nowhere near sturdy enough to do more than just hold in place. It also doesn't have any ability to really squeeze in like a corset does - without laces on it there's no ability to cinch in once it's on.
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