I concede, I'm wrong
It is interesting to note that if you are a warlock/wizard or wizard/warlock it behooves you to be a wand version of your class as you'll only need to get that one implement to play double duty. I'm not a huge fan of that, but whatever, RAW.
Tellerve
Only to save money, or for a shield. All the warlock and wizard implements can be used one-handed, so unless you can't afford it or have taken shield proficiency feat (why are you pumping you str as a wiz/warlock? Aren't you MAD enough already?), just use one implement in each hand. Works out well that way.
