The app also does not save the access tokens it gets back from twitter. They get thrown in a background job to be worked on, and once the job is done the access tokens are forgotten.
has two options for doing it without granting any permissions to a third party
I have no idea, why they do not offer a global show/hide retweets option. If you follow a couple of hundred accounts—like I do—having retweets enabled pretty much ruins your entire timeline.
Because it's in their interest to show you as much content as possible. Just guessing.