You load the rope, clip on the carabiner and off you go. Whether you are a beginner, or you have been climbing for a while, it is easy to use. There is a slot in the device for the carabiner to sit into once loaded, this seems to help with locking the rope when weighted.
I have tried to see if there is any slippage if, once the rope is weighted, and you lift up the dead rope to give some slack, and the rope is locked in there (we used a 10mm rope, please never let go of the dead rope, it is an ASSISTED braking device). Unlike some of the other non-mechanical assisted braking devices on the market, this seems to be truly superior than most of its competitors. A very intent and innovative design by Edelrid.
The way the Edelrid Jul 2 works is that when the rope is weighted, the rope pulls the carabiner up into the slot, wedging the rope tight to the device, locking the rope into place. When you want to release the device, you place your thumb in the thumb loop, tilt the device, you then release the tension, for either lowering, or paying out rope again.