That thing would be deadly as hell folded, It’s essentially a small club/mace.Page 9:
It's a folding fan. It can be more than a centimeter thick once folded.
This specific fan has 18 blades. At just 1 mm per blade, the whole thing will be at least 1.8 cm thick once folded.
And since the fan is supposed to be blunt, 1 mm per blade is a pretty reasonable estimate.
As an assassin’s tool, used to crack unsuspecting people on the head it would probably be harder to not do serious damage.