When even a linen dress shirt is too hot and a t-shirt too casual, the polo bridges the gap. I think untucked is more functional in hotter weather but tucked is more formal. Although, I like the look of untucked a bit better probably because of the way it fits. This is an XS sized polo in a 'Sports fit'.
Polo shirt - Rodd & Gunn
Chinos - Country Road
Belt - Herring Shoes
Derbies - Connor