Meguiar's #9 is one of the "hidden secrets" of local luthiers (multiple in my area use it) use to shine up guitars before returning them to their owners. Not used if the lacquer is cracked, but does an unbelievably good job on intact finishes. There is an exctremely fine grit in it, so fine that you cannot feel it if you rub it between your fingers, but it is there. It also acts as a chemical cleaner.
Simonize is like gravel compared to say, cement dust. Simonize is pretty uncontrolled in terms of how even the grit size is, and the grit inthe Simonzie polish is at least 100X bigger in terms of size. The Meguiar's Mirror Glaze products are really body shop supplies; they don't leave any residues behind that would interfere with painting a vehicle, and the abrasives are very tightly controlled.
The Meguiar's products all have numbers (#1, #2, #3, #7, #9, etc.) by intended use. However, the numbering system jumps all over the place, for example, the #1 is a Medium Cut cleaner, #2 is a Fine Cut cleaner, but #3 is a Heavy Cut cleaner, #7 is designed for use with paints prior to 1975, #9 is a Total Swirl Remover. But most people in the car industry would call a swirl remover a medium to heavy cut compound; the #9 is on the other end of the scale, as in one of the finest of fine polishes. So I haven't been able to find a pattern of any type in their numbering system. The descriptions are quite accurate; the medium cut cleaner (really a compound) is more aggressive than the fine cut cleaner (also a compound).