Sundowner® is the lesser-known sibling of Pink Lady®. On this website we tend to use the term "sibling" when talking about apple varieties with common parents. However unlike human children, apple siblings are nearly always raised in separate places by different growers, maybe decades or even centuries apart. However Pink Lady® and Sundowner® really are siblings - not only do they share the same parentage - Golden Delicious and Lady Williams - but they were developed at the same time by the same fruit breeder, John Cripps of Western Australia. Pink Lady® and Sundowner® are trademarks - the actual variety names are Cripps Pink and Cripps Red respectively.
Sundowner® is very much a warm-climate apple. That means it needs long hot summers to ripen, but it also has a low-chill requirement so it can tolerate winters where temperatures are rarely below freezing. (Apples originated in mountainous central Asia and need a period of very cold weather each winter as part of their annual growing cycle).
Sundowner® does not have the distinctive pink blush of Pink Lady®, being a more conventional "bi-coloured" red apple. The flavour is less delicate than Pink Lady®, and slightly more distinctive - in this respect it is probably the better apple.
Although primarily an apple for eating fresh, Sundowner® can be used in the kitchen - it keeps its shape when cooked. For an example see this recipe for Rustic Apple Tart.