I use zoom occassionally.
The zoom size is only marginally larger than Full size; I measured a periwinkle at 7cm (Full size) on my monitor, and 8.5 cm (Zoom). On my iPad the same periwinkle is 2.5cm (FS) and 4cm (Z). That surprised me so I checked again; same result.
Zoom responds like a compound microscope, moving the opposite way to the mouse/finger. On the desktop, with a mouse, that seems very normal to me; on the iPad, using my finger it seems confusing. That surprised me too. It seems my brain has learned right hand manipulation (as in using a microscope) better than finger manitpulation.