Fly Swatter allows Shoko to send energy waves and attack from a farther distance than her normal reach.
In order to use the Quirk, she appears to have to swing one of her arms very quickly, in which she could use it multiple times at once.
The farthest distance that Shoko has been able to use her quirk is only a few meters away from her. The force of these energy waves seem to be about the same as if a regular person were to do the same action at a closer distance. It is unknown if she could swat any farther than that.
- My Hero Academia: Vigilantes Manga: Chapter 16 (p. 8).