Most letterbox distribution is sold by delivery round or postcode. Those shapes were drawn for the post, not for your catchment. A radius is usually closer to what you actually want.
Australia Post unaddressed mail and the big distribution firms target by locality, postcode or delivery round. That works when your catchment happens to match one. It falls apart when your catchment is a circle around a shop, a listing, a clinic or a display home, which it usually is.
The practical difference: a 1 km radius around a corner store might cover parts of four different delivery rounds and none of them completely. Buying all four wastes most of the print run. Buying one misses most of the catchment.
The count updates live as you drag the radius, which makes it a print quoting tool as much as an address tool. Set the circle, read the number, multiply by your cost per thousand, and you know the job before you order anything.
Turning off Include units and apartments is worth trying if you are comparing costs. In an apartment heavy suburb it can halve the count, though in practice each unit has its own letterbox and you probably want them.
The CSV sorts by suburb, then street, then distance, which reads sensibly as a walk list. Print it, tick as you go, and you have a delivery record.
If you use a distribution firm with GPS tracking, hand them the list rather than a hand drawn zone. They get exact coverage and you get a count to check the invoice against.
Put in the address, set the radius, and see exactly how many letterboxes you are printing for.
