I just tonight decided to get the leads for this. They weren't too bad to get– most of them being solo content with the exception of the penumbral oil. However, I appreciate that the lead from Moongrave drops from seemingly ANY boss. That meant I could go through Moongrave solo with a companion and still expect to get the lead without having to try beating the entire dungeon.
All that being said, I really like this item. The concept is neat and I didn't think it would show up in a game like ESO. Very fun for adding stealth identity to our characters.