For me script is not working well. A lot of time xerath preparing Q but no shoot (even if enemy in range). Very often xerath Q going to different direction (Not to enemy). Combo not using properly QWE. I have to repeat "space" few times. :/
This might be because you're locking on your own champion and that makes everyone else not visible. External works differently. I put my combo on V and so long as the enemies are visible the prediction is near-perfect.