People talk about not over lining fish because it will spook fish. With mono/nylon, yeah, because of the sheen by the sun reflecting through the leader. And of course if you really over shoot it and over line it with the fly line, that will do it too.
Ever since I was talked into furled leaders I had my reservations as well. But after fishing them, and learning to take care of them, they last a long time. And I had noticed the fish are not shaken by them at all. I have watched my leader many times go right over the fish and it still came up and took the fly. I swear!
Furled leaders have been around for 100+ years. They worked back then, and they work today. I truly believe they are getting more popular.
Another thing I like about them is they land very softly, and are very supple. Plus, they don't spray water like a mono leader does when lifting it off the water. In my opinion, they are way above mono leaders today.
You'll find people who are set in their ways, and will tell you furled leaders are just a hype, and these people have never tried furled leaders. They speak through their ignorance. And there are folks who just simply prefer mono over furled, and there's nothing wrong with that.
Some furled leaders come impregnated with floatant, like Zen and Appalachian furled leaders. I hear Appalachian is a good brand and also guaranteed to float like Zen. But I have not tried them, so I can't really comment. But Zen I do use, and will say they are wonderful. I don't much like Cutthroat furled leaders. You have to apply floatant yourself.
Now, at times you will see your leader go under. It's the current pulling it under, or you may have dirt in your leader making it sink. It's good to rinse the leader out with cold tap water after fishing to get rid of scum or dirt from fishing.
I'm going to send you a PM with a tv episode of a person talking about leaders, and he does cover furled leaders and how to properly tie them, and their usage, and a little history. He covers different leader styles, and he's a different type of tv fishing host. In other words, his show keeps it real, and I like that.