I also like Monkey Puzzles, but don't think of them as "unusual" any more, so many are seen in gardens these days.

If you do have them, please have several, not one. They are dioecious, and the pollen only travels a couple of hundred metres or so, so you are breaking their fundamental arboreal rights by keeping them in isolation. Also you can't sex them until they grow up, which takes decades, so you need a copse to be sure of having a mix of the sexes. The nuts, which are huge, are edible if cooked. Plant them reasonably spaced out. In 50 years, they will look daft unless they are at least 10m apart from each other. In the mean time, you can plant plenty of other smaller trees between them.

In nature, they often grow in mixed forests with Nothofagus dombeyi. So there is a good reason to grow some N dombeyi along with them. The mixed forest of these two species on the upper slopes of Volcán Villarrica in Chile is a wonder to behold: the trees (of both species) are enormous (many with trunks a good 2m in diameter), far bigger than any seen in this country, and very many must be several centuries old. We are very lucky they got protected before they were logged.

As they mature, there will no longer be any sharp bits lower down. You could put a livestock fence around them until they were established, though that would take some decades.