Modern Isuzu engines run common-rail injection at pressures that leave no margin for contamination. Injector tolerances are measured in microns. A filter that does not meet specification does not fail loudly — it simply passes particles that quietly destroy injectors and the high-pressure pump.
By the time the symptoms appear — rough idle, smoke, a loss of power under load — the damage is done. A set of injectors and a pump will cost many multiples of a lifetime's supply of genuine filters.
The same logic applies to brake friction material, clutch components and suspension bushes. On a fully laden truck these are not places to economise.
Genuine Isuzu parts are stocked at all six TMD branches, with inter-branch transfer for anything not held locally. They carry manufacturer warranty, which counterfeits by definition do not.