I have been keeping a spreadsheet of fuel usage for my bikes, and may be able to answer your first query.
I have the IICE-Air units installed on both of my bikes; a 2002 R1150R with bags and BMW Touring Shield, and a 2005 R1200RT with a Hannigan sidecar attached.
Below is a graph showing the fuel economy figures for the R1150R before and after installing the IICE-Air.
Before installing the unit I had to run Premium grade fuel (93 octane) to control pinging if accelerating hard/suddenly; and it still did it on occasion even on Premium.
I did notice a slight decrease in fuel economy in mixed city/highway riding with the plug installed, but also found that I could run one gear higher at any given speed, so I gave Regular grade fuel a try again.
Running on Regular grade fuel (87 octane) I find that the bike still runs about the same as on Premium with the plug installed, including being less prone to pinging under hard acceleration.
As a bonus, the bike gets around 10% better fuel economy on Regular with the plug vs. running Premium before the plug was installed!
Drivability improvements and being able to run in lower gears is similar for both the solo and sidecar bike, but I have not been able to discern any solid pattern in the fuel economy with the sidecar rig because of the much wider variations in fuel use depending upon speed, loading, different size rear tire during winter/summer, etc., and not having put as many miles on the rig since getting the IICE-Air units.
One HUGE difference I have found with the IICE-Air installed in the sidecar rig is when taking off from a stop. Because of the extra weight of the sidecar I used to have to give it a fairly large amount of throttle/rpms and feather the clutch quite a bit to get things rolling.
With the IICE-Air installed take-offs take significantly less throttle and feathering. Nearly as easy as on the 1150R solo bike. Makes riding the rig in city traffic MUCH easier.
For me, that was worth the price all by itself.