Thanks. I'll definitely try it out now, especially when facing any invis heroes.
Another question- when I am trying to cast force staff (or any other targeted item, if I recall), the cursor doesn't indicate whether the target is in range (the purple tinge) or if I need to move before I cast (the little man next to it). Is there any way to change this / a key I can press to highlight the range of it? I find that when I try to initiate with the force staff (casting it on one of the heroes that is caught slightly out of position) I always misjudge the range, and the delay causes him to be pushed in the wrong direction.
(of course the main reason I get force staff, beyond it's general utility, is then I can make permanent wards by force staffing to a rune spot, relocating to a creep wave, tethering to a melee creep and bringing him back with me. Free wards for the rest of the game)