My engine is a 3.6ltr V8 diesel and I started to experience issues with the rev counter fluctuating between 600 & 900 rpm on tick over. On many occasions after a few minutes of city driving I would receive dash notifications that there was an engine management fault. I took the vehicle into my local JLR specialist garage only to be advised that it was very likely that I was experiencing an injector failure, and that all eight may need to be removed and cleaned. That's a 7 - 9 hour job in labour terms (say £500). A further specialist cleaning of injectors at £50 each, or new ones could be required, £450 each (plus reprogramming each injector into the engine's ECU). Absolute worst case scenario: replace all eight injectors. All prices + VAT.
Following a bit of research on injector / combustion cleaning products, and viewing web forums, I discovered AR6400-D, which I promptly purchased to try to resist a £x,000 garage bill. Added it to the tank in the prescribed ratio, and before half of the tank had been used, the problem had gone. The rev counter now sits without fluctuation where it should be, the commonly associated diesel clatter noise has gone, and the V8 diesel sounds much more heathy. I've not bothered measuring fuel consumption since I usually only receive between 14 and 27 mpg anyway. I made that decision when I bought the car (although it's "greener" than the car it's replacing).
I'm currently using a course of AR6200 and avoiding supermarket fuel, and although now slightly more expensive to run per mile, in the long term it should save thousands if that's what cheap fuel does to the injection and combustion chambers of cars.
Would absolutely recommend this product without hesitation.