Do stp cleaners work?

[gabriel2012]

Well today there was a sale at a local gas station on fuel additives made by stp
The cleaners were a $1 each so I bought two different ones since that was all that was left on the shelf by the time I got there.

I bought 1 Super concentrated fuel injector cleaner(black bottle)
1 complete fuel system cleaner

I plan on using the complete cleaner on my yaris and the fuel injector for my dads truck

the bottle says it treats 21galons and I know the yaris has 11 so I plan on using half the bottle (correct me if I shouldn't)

do these things really work or should I give them away?
(I plan to use it on my yaris b/c I don't know how well the car was maintained before I bought it) and if it helps my tank is only missing one bar, almost full