(Or similar approved) materials

Currently working on a nec3 project working as a subcontractor for a principal contractor. The form of contract is option b
The drawings details a certain type of hydro rake (or similar approved) in which we have found a cheaper product that meets the same performance criteria and this has been approved by the designers.
The principal contractors has sent a instruction requesting the saving we have made on the cheaper product. Is this right? Surely this would be a saving made by ourselves (subcontractor) and we would apply for the rate in the B.O.Q
Thanks in advance

if the product satisfies the Works Information then there is no saving due to the principal contractor because there is no compensation event

Thanks for clarifying Dave