The design of the Bosch Platinum +4 means that the spark is almost completely surrounded by metal. Compare that with a traditional style plug, on which the spark is almost totally exposed to the combustion chamber. It's obvious which design is better (for most engines).
I ran a set of the Ir Fusion in my car for a while. They are the same thing as the Platinum +4, only with some iridium as well as platinum (I think on the center electrode). I thought they'd be fine because I heard and read that BMW uses Bosch 4-tip plugs extensively. I hadn't noticed that the BMW plugs were also of the semi-surface fire type, which is very different from the Platinum +4: they do have 4 ground electrodes, but the center electrode sticks out way farther, so the spark is totally in the open. Once I realized this, I bit the bullet and shelled out again for the OEM plugs. The car ran noticeably better.
The moral of the story is, if the Platinum +4s are radically different from what came in your car, don't use them.
