I wanted to cast keen edge on a fighters weapon but only the casters inventory opened. The spell discription says it has range, shouldn't I be able to cast it on a target and the targets inventory should open to select the weapon ?
Unfortunately, the game doesn't allow you to target an item that another pc or monster is wielding directly. So the fighter will have to transfer the item to the spellcaster, who can then cast Keen Edge and then hand it back.
I use it as part of my buffing routine; it seems to last longer than most buffs I use (e.g. Barkskin, Magic Circle) if you don't map travel/teleport. The only downside is there is no tab on your portrait icon for you to track it, but you can check the inventory of the character (i.e. Shortbow 17-20 x3) or the confirmation rolls in the combat log to verify.
Strictly speaking I've been using the Horn of Good, but yeah, seems to be working fine - deflection bonus to AC etc. - at least as a defensive buff. I haven't tried using the spell with an enemy as the subject.
My cleric used to use it as a spell on himself until I realized it wasn't working. I guess I expected it to work like the old PnP spell Protection from evil 5' radius.
It does have a radius, each NPC covered in the blue circle benefits from the buff - I usually have it on my flanker/pointman.
My ftr 1/cleric "n" performs the tank function after prebuffing as needed. My barb 2/ftr n and my ftr/rogue are too busy running around killing important targets.