Transmission

After clicking on the new option in preferences, it would be helpful to have a confirmation. Maybe something next to the button--green dot or something.

That would require continuously monitoring the default app for these links. Not worth it imo.

even without giving ongoing accurate info about whether transmission is the default app or not, i think that some kind of response could be provided to show that the change has been made now. whether it's a popup "success" dialog or some temporary change to the button or text in the window, or some other way to show "this action has been performed right now" without needing constant monitoring. having a button click give no feedback at all isn't very reassuring.

not a big deal for me if i'm honest, very low priority, but just an opinion

I'm going to disagree on this one.