Considering it's an anti-binder PrC, I can't really see someone who's got all 5 levels in witchslayer putting a feat or level into Binder. Would fully expect the DM to throw a book at a player who did that, even if it is allowed by RAW.
Does that work on Dimension door as well? Or only on spells with the word 'Teleport'. How about benign transposition or whatever it's called.
Already made that point. Was told to make a paladin of tyranny/hexblade with ability focus.
It's one of those things that's more likely to become useful if used by a higher level NPC on the party, rather than by a PC on anything but a mook.