It does work - I use it on every tank of petrol.
Keeps the injectors clean - this is an issue with LPG
This is probably more of an issue.
Engines simply don't get excessive carbon build-up internally these days because the mixture is always spot-on and they don't burn oil. Also the combustion chambers run so hot that no more than a minimal thickhess of deposit will ever build up. Petrol is clean, with no added lead and the like so it's a non-issue.
You can get issues with the injectors when they run for a while then dry out because the fuel can leave deposits as they dry in a hot engine. Having said that, I've taken injectors from wrecks in scrap yards and never had one that didn't have a reasonably good spray pattern when tested.
All other parts of the fuel system run wet even on LPG so they don't have an opportunity to get dirty.
Kevin