In my area, some people cut the feijoa tree into balls every year. This way, if ever there is a cold spell, it is easy to put a transparent winter cover over the trees. This also protects the flower buds. But in my case, this pruning is more for the sake of beauty, because cold temperatures of -15°C are very rare or of very short duration. I'll post you some pictures when I go for a walk. But don't worry, they're pretty tough, mine can easily withstand -12°C without damage. And even once -20°C but only for a few hours, but on already mature trees. But if it didn't die, there was damage that time.