The difference
What each option actually means
A pressure-reducing valve controls downstream pressure; a hammer arrestor is designed to absorb pressure surges in suitable applications.
The trade-offs
They address different mechanisms and may not solve pipe movement or faulty quick-closing valves.
How to decide
Measure pressure and identify which event causes the noise before selecting equipment.
Before choosing
A plumber should assess suitability, condition, access and applicable requirements. Product or repair recommendations made without seeing the property are preliminary. Ask for the proposed scope, exclusions and relevant warranty details before approving the work.
Little Bay Plumbing can discuss the choices with you and help plan the next step for a Sydney property, subject to booking availability.