Fuel Additives for Diesel and Petrol engines whats best

I have been pro fuel/oil additives since I heard the story of a vehicle travelling from Adelaide to Sydney after the oil and additive were drained from the sump and measurement indicated no wear on the cylinders. I have also used the model where you turn a handle and 2 bearings move. One bearing turns in oil and the other has the additive. You can notice the difference. On our Landcruiser and small Corolla hatch, diffs, gearboxes, and engines have the additive.

In regard to Fuel, I have used Nulon, for the Petrol and Diesel engines in the main to clean the injectors but recently have tried Chemtech Diesel Fuel additive and Valvoline Fuel (unleaded) Injector and Carby cleaner. My problem is that unlike the oil additive where I can see/feel the difference, the fuel additives are a lot harder to determine the benefits.

It may be a bit like smoking/cancer 1 smoke does not kill you but 20,000 will put you under. One dose of fuel additive does not make a difference, using it on every tankfull will delay an injector replacement by say 20,000k. On my turbo diesel Cruiser I change the fuel filter every 5,000k so this could mask the benefit of the fuel additive also.

Would appreciate your comment on Fuel additives.