Feijoas are a really hardy fruit tree. They can handle dry coastal conditions (once established) right thru to damp winter clay. They do grow best in full sun but will grow quite happily in half-day shade as well. They grow reasonably quickly into a good-sized shrub/small tree at around 4M tall, and 3M wide. Or they can be kept smaller with regular pruning or trimmed into a hedge.
All varieties (apart from Unique) fruit much better when planted with another variety to pollinate them. And as the varieties all ripen at slightly different times, you could buy one of each and get a long feijoa fruit season rather than a glut all at once.
Varieties generally available are:
Unique
One of the earliest ripening varieties, Feb/March. Very sweet and juicy, medium- sized fruit. Self-fertile.