Thank you for your appreciation and feedback!

> If I post with jumble while looking at a certain relay set. Does it post only to that relay set?

Jumble will send your notes to the write relays you have configured and the relay set currently in use. For replies, likes, etc., they will also be sent to the read relays of the mentioned users.

> In Relay settings > Read and Write Relays it was unclear if editing this would change my settings globally for other clients, or just in relation to relay sets (I had to delete some things to check, and then re-add them).

It will modify the kind 10002 event, which may affect other clients that also use the kind 10002 event.

> Perhaps when posting a note on Jumble I could have the option to post only to the relay set, or to post to global relays.

I would be happy to add this option. As for replies, they might still need to be sent to the read relays of the mentioned users, otherwise, they might not see your replies.