Ok so it seems that the p60 drop ins are all the rage right now. But why? Aren't there more efficient reflector configurations available? Other than the ability to swap out reflectors and emitters quickly whats the big deal?
Does the p60 drop in perform that well?
The way you phrase your questions indicate that you may not fully understand what "P60" drop-ins are.
The P60 (type) drop-in is nothing more than a form factor of certain dimensions that will fit a particular range of lights, most notably the Surefire 6P among MANY others.
Beyond that, no two P60's are alike, and they differ in LED's used and the design of the reflector and the material the reflector is made from.
That means that, among the many P60's available, there is great variation in brightness, beam shape and spill, and how well the drop-in can take the heat.
So the short answer is that what's so great about the P60 drop-ins is that there is a very large selection to choose from that offer different lighting characteristics from each other, and there are many choices of "hosts" in which to install the P60 drop-in in.