I don't think using your own GPS is legal
No hand held unit is IFR capable and not usable for Class II navigation
IFR capable GPS requires an STC
The using of non-approved GPS will not be allowed by any POI-or equivalent official--in the OpsSpecs.
Therefore, I think it's incumbent on the PIC to follow the guidance of the AIP regarding navigation equipment required in said FIR---and adhere to the COMPANY'S OWN APPROVED OpsSpecs
