I rarely buy airmiles, but did succumb to a BA offer last year. I tend to travel BA, as I am based in London. I use seatspy, which is pretty good. I am on various apps, one of which, and I can't remember which, told me BA had suddenly opened up more Avios seats to Sydney. I only had 30 mins, but booked a business class seat, Sydney return, normally very rare, for reduced Avios.