I love ferreted leaders... I use them under all sorts of fishing, from saltwater to lakes to trout streams. For my Tenkara Rods, I use a 12 foot ferreted leader as my fly line. Unless you make your own, they can be expensive.
This is how I teach fly casting to the Boy Scouts. We use the TFO "Scout" rods. It's an 8'6", 5 wt rod with a WF-5-F line. I use a 6 foot piece of 15 or 20 pound test fluorocarbon as the leader. It turns over a big fly well, and we don't get as many wind knots in the leader. ( with 20lb leader the wind knots are easier to untie too. LOL ) The big flys are just right for "hooking" the Back Yard Bass we use as targets. I still use a straight piece of 5 or 6 foot straight mono because it works well for big flys and bass bugs, Most peacock and largemouth are not that leader shy. So it works fine.
"Why let the truth stand in the way of a good fish story?"