I've tried small corset with hooks (small), and lace up corset.  Very unimpressed with the result.  Did not use as a "trainer," but it seemed illogical to expect such a thing to "reshape" my body.  My own approach became to shed any visceral fat that I had accumulated from years of high carb, high insulin, high cortisol living.  It took about 3 years, but I can honestly report that it is possible to shrink your waist, even in your 60's, without losing any muscle mass that can be used to accentuate a feminine form.  Small waist just seems ultimately feminine to me.