This extension does nothing special. You manually choose the conversations to delete and then the script deletes chats one by one through the same dialog box. Therefore in practice it is faster to delete everything manually.
The reason I gave it 1 star is that after around 10 deletions with this extension chatgpt limits access because "You’re making requests too quickly.". So the extension not only doesn't really save your time, but may also be a reason for a temporary ban.