The red circle thing is actually slightly bugged. The AoO trigger radius is slightly smaller than the display, so you can move to a white circle, but get with an AoO anyway.
As far as it triggering for the player, I've got a guy who has that Talent and it seems to be working reasonably for him.
Casting and shooting weapons in heat of battle should not be so easy:
Ranged shoot, or cast provokes attack of oportunity.
Yeah using a spell or a missile weapon within striking distance of a combatant using a melee weapon should provoke an attack of opportunity...I am really surprised and dismayed that it does not.
Generally, I think this is an okay idea. I do not think that it should be applied as a blanket effect to everyone.
Rangers by definition should usually not be in melee range of enemies to begin with, but I'll put that aside.
If the AoO rules were to be changed to include ranged attacking and casting, I think that touch-range skills, and self-target-only effects should be exempt from provoking AoO's. Touch range for the obvious reason that they are MEANT to be used at close range, and self-target-only ones for balance reasons. I'd also go as far as saying casting healing spells should also be exempt.
I also think that movement/escape skills should also be exempt from provoking AoO's, because they are meant specifically
for escaping an enemy without provoking an AoO.