Most people's tanks will have an accumulation of crap in the bottom, so probably not a bad idea to pull the tank and flush it every two years, it's not a big job, so worth doing. As far as conditioners go I really don't know what to believe, but there are more harsh chemicals you can run through the system, BUT you need to bypass the fuel filter and run it directly into the system. This apparently cleans the injectors. There are risks involved with doing this, if you enter a contaminant into the lines when you have them open you can F things up pretty good. If you do it all according to plan you should have sparkling new injectors that perform as well as new ones.
Well well Bull........ sorry I can tell you they don't work, I have done numerous testings and noted l/km over many tanks after various additives and they simply don't do a thing.
The best thing to do is get a changeover set or new set of injectors, and that will bring a new lease of life to the vehicle and bring back long lost fuel economy.