S19 used Xiggi method as well during the summer before junior year. He busted his butt. Probably studied 10 hours a week for six weeks. Took practice tests four times under real conditions (at the library with the right timing). I proctored the test for him. It worked. 740 EW 800 Math.
I guess I should say, too, that he didn’t do any PSAT-specific studying. He did find that test a bit quirkier (taken two months after his SAT). He managed a 221 which will be NMF for our state if the cutoff doesn’t change but, weirdly, his math was the section he did worse on. There were stats questions on there that were not part of his SAT studying and he got three questions wrong. He had a perfect math SAT with all questions correct. I still wonder if I should have had him look over PSAT practice tests but we thought the PSAT would be just an easier version of the SAT. The reading and writing sections seemed similar but easier (and shorter) than the SAT but that math threw him off.