No not used that product but would ask how the vehicle is driven ?
Senior citizen going down to the shops and back wont get the engine hot enough to blow out the cobwebs.
As a diesel is it getting the usual service done including fuel filters ?
I do remember a long big air hose splitting on top of the engine and reducing performance.
Does your model have a DPF that is blocking up as not getting motorway driving and putting it into burn mode if needed.
Diesel owners buy cars not knowing they need driving on motorway .
Cataclean was one we did use , Dipetane is another one that Taxis use.
One of the last times i used Innovation Powerkleen now rebranded as Novafuel Powerkleen as put some into the fuel filter and the rest in the tank , one big rev and left a 6ft black mark on the floor. 2008 Ford Galaxy 475k miles and passed on emissions in our NCT , think the lads thought their machine was bust.