Why are you using this additive? Do you have a fuel-related problem? Don't try to fix something that is not broken! Maybe if your engine is hesitating or idling rough, additives can help. Or maybe there is a vacuum leak. Or maybe it just needs a tune-up or new fuel filter. Proper diagnosis would be my recommendation.
Most top-tier gasolines contain everything needed to maintain a healthy fuel system and do not need any more additives. Oil companies usually spend a lot of money and time developing their formulas for fuel and motor oils, but the DIYer always thinks he can make them better. Maybe we can, but is any perceived or real benefit worth the cost? There are exceptions such as long-term storage, ethanol (water), bad gas, etc. Additives can be very helpful with these situations. Fuel system cleaners are OK for occasional maintenance if you really want to use them, but again, additives should not be required if the engine is getting regular maintenance.
Sometimes a good hard flogging will make an engine run better, this is known as an "Italian tune up" and it works mostly for cars that are driven like grandma all the time or engines that only see occasional use (sit for long periods). It just blows some of the accumulated carbon out of the combustion chambers. Also, it is fun.
The local tire shop recently recommended a fuel system cleaning for $110 based only on my vehicle mileage. I can't blame them for trying but they aren't getting my $110. It runs smooth with strong power and good fuel economy, it doesn't need the treatment. I do use Lucas in the gas every couple months, a family member bought me a gallon as a gift awhile back and I'm working through it slowly.