I love the way they turn over, but their use for me is only for floating bass bugs.
The reason is: if you have weight on the leader, or a heavily weighted fly, when you put tension on the leader it begins to untwist and spin the fly during the retrieve or drift.
I first noticed this on clouser minnows and at first I thought I was tying my clousers wrong. But if you grab the leader and pull on it you'll notice how it untwists as you pull. I don't want my fly spinning through the water.
They do turn over bass bugs like nothing else though, so I still use one if I know I'm going to be fishing poppers or hair bugs all day.