A hands-free waist system with a retracting line, so the dog can range a little further ahead on open ground and the slack comes back in on its own instead of dragging.
Reflective nylon with an adjustable belt, six options. Locking mechanism on the reel.
Honest limitations of a retracting line
A thin retracting line gives the dog constant light tension, which teaches them that pulling is normal. If you are working on loose leash walking, this will work against you, and a fixed-length leash is the better tool.
It also gives you far less control in a sudden situation than a fixed leash does, and a thin line under load is unpleasant to grab bare-handed.
Where it does make sense
Open trails and beaches with a dog whose recall is solid, where you want a bit more range than a 1.8m leash allows but not the full commitment of a 10m long line. Lock it short before you reach anywhere busy.
For recall training proper, use the Training Long Line instead.