In reply to Phil Anderson:
That´ s the problem, the roller diameter is too small really for 180° applications. It´ s better than a 10mm karabiner though by about 12% and miles better than some of the real thin karabiners which go down to near enough 8mm.
The other problem is under high load thicker ropes tend to ride up onto the spine and rub, there´ s some photos of a worn one on one of the US websites somewhere which was used for top-roping. For reducing drag on wandering lines with only rope weight it´ s fine but for hauling not a replacement for a larger diameter pulley.
For jumaring the ease of putting the rope in and out is great but I use a conventional pulley instead, I´ ve usually plenty of time and not enough strength!