From my experience, "tax free" in most airports is snake oil. It either doesn't exists or the price is inflated and the total price matches the street price.
Unless some notorious place for alcohol and I think cigarettes, electronics are not very "tax free".
Few examples:
JFK perfumes, matches street price
JFK electronics: not many, over the street price (or amazon)
SLC perfumes, matches street price
IST alcohol is way way lower than street price (but alcohol is extremely taxed in Turkey)
Haven't been to Singapore in a long time and never been to AUS. But visiting around 30-40 airports yearly and duty free isn't that duty free anymore in most cases. Maybe Dubai and Doha, but again, for electronics I doubt so.
This apart from the 15 (PM) scarce availability.
You can get it cheaper if you fly to a low tax state in the US and just buy it. I'm flying from Poland to NYC next week and I have my in store pickup. The flight costs was the price difference between PL w/ VAT and NYC w/ 8.8% tax, $420 diff for a 15 Pro 512. It's crazy