What this checks

Every common device at once, not one at a time. You pack a bag, not a single item.

Three things are checked for each, not one. Whether the voltage will damage it or merely starve it — those are different answers, and most guides give the same one for both. Whether the plug fits. And whether the earth connection survives, which almost nobody publishes: a Type C plug slides into a Type F socket perfectly and carries no earth at all.

Country data is graded and labelled. Where it says two general references agree, that is what it means — not that we checked with the national authority.