Excellent program if you use it with accurate case (fired case capacity to the 1/10 gr. h20) and barrel length information (from boltface to crown to the 1/16th of an inch).
In combination with the OBT approach to finding a node (generally within 1/2 grain of the predicted load), it has been an effective tool for showing me what powders are potentially going to be my best within a reasonable load density.
I will say that given the lot to lot variation in powders, the velocities that it predicts are not always dead on. I recently used QL to give me a starting point for load development with VV570 (to see if it will give me higher velocity than Retumbo) in my 338LM Ackley Improved. It was predicting laughably low velocities (close to 100 fps slower than I was seeing in real life with my Ohler 35P), but the predicted node and pressure curves were exactly whereI would expect to find them.