I have grown these in New Mexico, both at 7000 feet and at 4700 feet. At 7000 feet I had several plants and they produced fruit regularly. I didn't see any problem with cold hardiness.
At 4700 feet I have several of these but only one is big enough to flower, which it has done regularly. We've had temps a few degrees below zero. I was concerned because I wasn't seeing a lot of fruits forming but I see now that they will do better with some other ones nearby. However, my plant did produce about 5 pods even with no other nearby tree.
As for eating these, I found them pretty bland. They are hard to open because the shell of the nut is soft, so you can't crack it. I ate some of the seeds raw and no, they didn't taste like macademia nuts. They didn't have much of a taste at all. The fact that they didn't taste like much and that they were hard to open discouraged me at first and then I found the secret!
I tossed the seeds, shell and all, into the blender with some water and pulsed the blender for a minute. I then strained the resulting "milk", which did a good job of removing the shell. The result was a nut milk that was nutritious if not delicious.
I didn't try roasting and salting the nuts.
One special point about the plant is that it seems to be extremely drought resistant. This came as a surprise to me, as it wasn't listed anywhere. When I left the property at 7000 feet, the yellowhorns were on there own. With no watering and only about 17 inches of rain a year, the trees were still thriving several years later.
