I REALLY like these chairs  

Niiiice!
Ooooooo, those are really lovely. You're right very sculptural.

No you must have six
arrayed around a glass top table like the petals of a flower and you'll need to get in the habit of keeping them perfectly arranged when not in use. Cool.

Why aren't there more...
...
three legged chairs? It seems like an obvious solution to getting lots of seating at a round table but I've not seen many over the years. Is it unstable or awkward to sit in?

It doesn't say
when these were made, or who designed them. I'm quite curious. . .
Wegner made a three-legged dining chair, I believe. I think a chair with one leg in front isn't a bad idea. A chair with one rear leg invites an upset, however. Or have you had a different experience ?
P Starck's three-legged bucket chair of a few years ago was handsome; the rear leg was "way back there," though. A local new restaurant got rid of theirs in favor of something more compact, I noticed.

They're designed by Kurt...
They're designed by Kurt Østervig (look in the item description. Try the link again and then type Kurt or Oestervig into the search box. He's made some beautiful pieces of furniture, there's even a version with four legs of this chair up for auction.

My take on it...
...is that Kurt Østervig's "spisestole i palisander" are more part of the decline of mid-century danish furniture design than of the "golden age". They are without any doubt very elegant and well made, but they also show a kind of virtuosity that introduces the decline of every great style period. In the balance between innovation and mannerism there is just too much of the latter. Raising the tips of the backrest wings less, might have avoided that.

Thanks, M_
They are a bit flamboyant, aren't they. . .