I know it's easy to be skeptical. I'm exactly the same way and usually have to do things for myself before believing, but when I was a rep, we have done the testing. I have represented 8 different brands including Berryman, and that was the last one we had until I left the rep business. Here's the information and ways to test. Give them a try for yourself and post what you find. I think you'll be quite impressed both by the tests and once you use it in your car.
Polystyrene is the main thing that fouls fuel injectors as a by-product from gasoline. It shows as varnish, which you see on old carbs that have been sitting for a long time. Most FI cleaners are nothing more than kerosene with a tiny bit of diesel fuel mixed in for lubrication (Gumout, STP, Valvoline, etc.) and this has absolutely no solvent properties in regards to dissolving the styrene coating on the injector body and cone. If you want to test for yourself, buy several different types, and buy a can of Berryman. Set up styrofoam cups (polystyrene) one for each bottle, and pour a little bit into each cup. Pour ALL of the others first and when you get ready to pour the Berryman, put the cup in a bucket because it will dissolve the cup instantly and pour straight through. The second test is to find an old carb from a small engine or car that is all varnished up. Pour a little from a bottle in and wait 2 minutes and then see if you can notice any change. Try ALL of the other cleaners first, and then pour the Berryman in and wait 2 minutes. You'll have a clean, varnish free area wherever the Berryman touched the carb.
Run your car down to about 1/4 tank and pour the Berryman in. Drive it until the FUEL light comes on and then fill up with good Mobil or Shell 93 Octane and run that tank just until the FUEL light comes on. You'll notice a big difference for the next 15-20 tankfuls.