I really don't understand the marketing approach. What cleans the "Fuel System" must also clean the "Fuel Injectors" - they are making "newbies" think they must run a "Fuel System Cleaner" as well as "Fuel Injector Cleaner".....but yes, under most circumstances they are typically the same thing, maybe just higher concentrations....
I know in my early days of MSDS surfing, I was looking at the various MSDS for the "Gas Treatments" (i.e.: STP red bottle, Gum Out white bottle, Super Tech red bottle, etc...) and they were almost all the same formula(s); typically high doses of kerosene (jet fuel! is how STP likes to market it).
Then, STP has the "Fuel Injector AND Carburetor Cleaner" so, I took a gander at that....and of course, Gum Out, and SuperTech have their own bottles too, to "follow the leader" lol....and yea, again, the composition was about the same.....in fact, almost IDENTICAL to that of the "red bottle" - again, largely kerosene....
The STP Black Bottle though, that has a little bit more "Oomph!" - at least more so than the red bottle....
Basically, the "Fuel System Cleaners" are typically in larger bottles (or larger concentrations) than the fuel injector cleaners, which are usually in smaller bottles.
Much of this is purely marketing....our fuel isn't as bad as it used to be....so the majority of people probably don't even NEED these chemicals in their tank every fill up, but the companies still market them the same way.
And now the new fad is the "Ethanol Treatments", Lucas, STP, Sta-Bil, etc....all have their own line of product(s)
Personally, I'll keep on using my MMO and/or TCW-3 (if I forget the MMO)...