Most are solvents that will do a mild job of cleaning the fuel system as it moves through, but how effective is up for debate. Most of these solvents will burn off in the combustion chamber, so they aren't very effective for cleaning beyond the injector.

PEA based cleaners don't burn off so quickly, so they can do a decent job of cleaning the combustion chamber beyond what can be done with normal gasoline, making them far more effective as a "Tune-Up In a Bottle" that these products are advertised as. This is the chemical that made Techron fuel so good for so long, but their patent expired about a decade ago and then companies like Redline, Gumout and Royal Purple started releasing PEA based injection cleaners shortly afterwards