One of the hardier subtropicals -- it should grow anywhere citrus can grow, I would imagine. (But not in snowy, icy regions.) Certainly it has never shown the slightest damage in my Northern California garden, even during the worst freezes. (However, in my location 26F is a reasonably severe freeze.)
I have heard the taste described as "weird apricot" and, based on the fruit I have eaten, I would say that is about right! They probably would not appeal to all tastes. (Having said that, as far as I can tell this is mostly a wild-form fruit -- if anyone bothered to breed it for better fruit quality, there would most likely be a good potential for improvement . There are clonal selections available in Southern California.)
For those in the S.F. Bay Area, there is an abundantly-producing thicket of kei apples on the rare fruit peninsula at Quarry Lakes Park in Fremont. (I have been told that it is fine to sample fruit there so long as the fruit is ripe and abundant.) It is a bit of a walk from the parking lot to the rare fruit collection, but it is worth the trip!
Richard, I feel pretty confident that those are the most tightly-controlled kei apple plants in the history of the world...