I've just started using my "new" bottle of FP3000 I purchased a while back. Before that, I was using my first gallon of FP60 (which lasted about 2 years!).
I admit that my switch from FP60 to FP3000 probably took place at around the same time that winter gas phased out in my area. I have, however, noticed that my "maximum" fuel economy is notably increased versus FP60 in the previous two summer seasons.
My vehicle is not used for any daily commuting so looking at whole tank or "average" fuel economy is a difficult way to judge the effectiveness of products like FP. Sometimes my wife burns all the gas running errands. Sometimes I'm driving on road trips. Sometimes I'm doing all the running around and feeling "sporty" which obviously isn't good for "tank" mileage. My vehicle indicates a real time and resettable economy display. I have found, based on 7 years of driving this car, that my real time economy is substantially improved in steady-state conditions compared to FP60 or no additives. In a given situation (130kph, up an incline, maintaining speed, for instance) I've become accustomed to seeing certain real-time readings and they are significantly improved with FP3000. In fact, every time I glance at the real time (except bootin' up through the gears at high revs) they read better than I'm accustomed to seeing.
I'm using FP products mostly for cleanliness, but especially in these days I appreciate any increase in fuel economy. When I do embark on cruise-control highway trips, my "trip" economy is also great. I haven't had any truly rural (ie. 50-60mph) highway trips yet this season which is usually where my fuel economy goes through the roof. It is already substantially improved on my "interstate-class" highway trips (ie. 65-85mph).
In my case, my engine and software calls for 91 or 92 AKI. I've found in my area that Esso 91 gives both the best performance and fuel economy (both are important to me). I used FP60, now FP3000. I don't intend on dropping to 89 AKI (the lowest my engine allows) although I may be able to with FP. As I indicated, I am as concerned about performance as economy.