A few of my customers are chemical engineers attached to a leading petroleum company, who're very familiar with the formulation of fuels, additives and various lubricants. and being hardcore, highly fastidious owners with a technical background, they go to great lengths to locate fuel system cleaners for their own cars.
They only purchase those from Redline (the SI-1), from Bardahl (a top class but forgotten brand), and the Russian/Ukrainian Zado (very popular in Penang).
In Malaysia, these 3 are the easiest to purchase fuel system cleaners that contain PolyEther Amine, the strongest nitrogen-based cleansing agent in the fuel cleaning additive industry.
It is widely known that this cleaning agent is the only one that can give decent results in direct injection engines where the high heat + pressure within the combustion chamber can cause very stubborn deposits that cannot be removed by other cleaning agents such as the older PBA or PIBA. Some cleaning agents, such as PBA, can even cause a buildip of new deposits (!!) (Thanks to Lim of Shell for this non proprietary general info).
Even worse, the lowest end products use mainly solvents such as Naptha, and Benzene as cleaning agents.
Hnece, on my vehicles, I use only Redline S1-1 and occasionally XADO.