Sorry I may be off topic as the below is not a segula bit a statement of fact.
The Sefer Hachinuch writes; One who is careful with the mitzvah of Birchas Hamazon will always have Parnasah in abundance and in a respectful manner. One who wants to be careful should always bentch while reading the words in a siddur (or bentcher) and not bentch by heart. Shulchan Aruch w/Mishnah Brurah 185:1, see also Be’er Haitaiv
I haven’t found a translation of the Chida, happy hunting