Here are two other aspects that I think are important:
1. The prices for the new Speedlite 600 flashes with radio-control are not (yet?) Overpriced. I have therefore initially decided to use a slave flash, especially my camera (EOS 60D) a (optical) Master function possesses. If in the future a second flash unit is due, but it will then probably be a master flash.
2. The (optical) Master function of EOS 60D operates reliably indoors even without direct line of sight to the slave. But you have to know that some functions of the flash unit can not be used in the unfettered operation: HSS (High Speed Sync) and flashes on the second curtain.
3. The Amazon product description indicates: "In combination with a compatible EOS model, each setting for the Speedlite 430EX II is directly on the camera's menu system quickly and intuitively controllable." But that does not apply to off-camera flash: In this case, the 430 EX II is _not_ using the camera's menu controlled.