Short answer: yes, more than blinds or curtains in most Queensland rooms — but it depends on the window's orientation and how the shutters are used, not just that they're installed.
Why they help
Polymer plantation shutters sit rigid and close-fitted in the frame, which cuts down on the gaps around the edges that let radiant heat leak past curtains and most blinds. The louvres also let you control airflow and light angle independently — closed but angled to deflect direct sun while still letting air move, which fabric window coverings can't really do.
Where they matter most
The biggest difference shows up on west-facing windows catching direct afternoon sun. A well-fitted shutter, closed during the hottest part of the day, meaningfully cuts the amount of direct heat radiating into the room compared with an open blind or a lightweight curtain.
The trade-off
Shutters are a bigger upfront cost than blinds or curtains, and they're a fixed installation rather than something you can easily swap out later if your style changes. What you get for that is durability — polymer doesn't warp, fade or discolour the way timber or fabric can in a hot, humid climate — and a fit that actually seals the gaps that let heat and light through.
Bottom line
If you've got a room that cops harsh afternoon sun and you're tired of closing curtains at 2pm every day, shutters are one of the better fixes available. For rooms with mild or indirect light, the difference is less dramatic and a good block-out blind may do the job for less.