I began using FP Plus in my Cutlass and Tacoma a few years ago, I saw the most benefit in the Tacoma...smoother idle, easier/quicker starting. We bought a 2014 Accord Sedan that my wife drives a lot of highway miles for her job and except for the first few tanks, I have used it religiously with every fill up. This is my initial adventure with a GDI engine and I can say without hesitation that the injectors are not as loud (acoustically) as other Honda's of the same type I have heard. It's just my opinion, but this is a good investment if you are a buy and hold kind with your vehicles. I don't have any concrete science yet, the Accord just clicked over 42K and it gets 30-33 mpg. I plan to borescope the intake around 50K miles to see what kind of buildup GDI Hondas accumulate and take the plugs out to look at the cylinders and chambers/valve faces.
I am in Texas so shipping isn't real bad, I buy it by the gallon and use at the recommended dosage and will continue to use FP Plus.