Clamp mount or grommet mount — which should I choose?

Most single arms ship with both a C-clamp and a grommet base. Reviewers favor the clamp for desks with a usable rear edge under about 2 inches thick, and the grommet mount when you have (or can drill) a pass-through hole for a more permanent, flush install. Verified-purchase reviewers note clamp installs are faster but can mar thin or hollow desktops without the included backing plate.