I seem to recall this paint works by reacting with air to form a crispy, waterproof shell whilst normally, it's just like jelly. This meant that when you tried to grip to it with any substantial weight, the crispy bits that you're gripping to would just break and glide over the underlying jelly bits. Hence you'd never get anywhere... I could be wrong though.
Yep, it has been around for quite a while ...the owner of our local sweetshop used to paint the ledge of the front window of his shop to stop us sitting there when he had taken all our money for curly wurlies, refresheres, sherberrt fizzes etc....more than a decade ago.
Nasty old geezer.
I was under the impression that the paint actually goes on the top of the wall, and never dries. So it doesn't stop you from climbing, but if you do, you'll get covered in paint that I would guess wouldn't come off you or your clothes in a hurry.