Better the fuel additive, worse is the impact on your engine... sounds funny but it has logic behind it. With passage of time fuel injectors develop carb on the pintles. Every time an engine is turned off, the last drop of fuel dries on the pintle and scaling is formed. Baked with the chamber heat, the scaling becomes hard to dissolve. Fuel additives are strong solvents. when added to the fuel tank, their first action is to dissolve the scaling formed in the tank. Better additives make more cleaning by dissolving more scaling. The entire gunk which is loosened up, passes through the fuel filter attached to the submersed fuel pump. Some of it is deposited on pump filter and it is chocked partly. Some of it passes through and gets stuck in the main fuel filter making it dirty too. Little quantity which succeeds escaping from both the filters, pass through the fuel rail, injectors and is finally drained into the engine.
The fuel additive which is mixed in the fuel, passes through the injectors and dissolve the scaling present in the injectors. This dissolved scaling which is abrasive in nature is also drained into the engine. That is the reason all the professional car maintenance websites recommend change of engine oil and oil filter after usage of fuel additives.
On the other hand, in the off car injector servicing, the injectors are removed from the car and cleaned with the acoustic technology. This process influences only the baked-on deposits in the pintle of the fuel injector. Fuel pump filter, fuel filter and the engine itself remain safe.
I recommend following article to those who want to have more knowledge about injector cleaning.
Troubleshooting & Cleaning Dirty Fuel Injections