Drop-in = not much difference. Waste of money, to me.
CAI = open-pod designs, depends. For instance, in the hot 335 engine bay, a Gruppe M cannot work as well as thought, despite the good quality carbon fibre built and design. It could not isolate the heat from the engine. Hence, ironically, the Cold Air Intake actually sucks in hot air. I had the Gruppe M in my 335 - I could barely tell the improvement. Contrast this to a simple AFE open-pod WITH A WELL DESIGNED HEAT SHIELD built around it - the shield could actually block out some of the heat from the engine.
In short, it is not the product per se, but what subtle modifications your installer can do on it. For instance, if you really wanna explore deeper, try to talk to experimental guys like Rod (R2D) on heat shield wrap (reflective fabric type) or to construct a aluminium plates to block out the heat from your open pod.