Using the pull spring method instead of pushrods on a DLG is a great way to save weight and to create a precise, slop free linkage for your tail group. Using servo pulleys instead of servo arms can improve the resolution and the holding power of your control system. This is possible because the pulley has a constant travel radius that improves the linkage geometry.
For instance, let's say we have a 15mm control surface deflection and we are using a standard servo arm and control horn as our linkage. Next we remove the servo arm and replace it with the pulley and find the deflection has grown to more than 15mm. So we increase the length of the control horn to reduce the travel back to 15 milimeters. As we know from experience, using longer control horns reduces control surface travel and increases torque. This is how resolution and torque are increased by using pulleys.