I think they were withdrawn from sale a long while back after proving unreliable. They were sometimes called an American tip, I don't know why.
They were designed to fit very closely just behind the coronal ridge, and of course worked better for those with a very pronounced corona. They were extremely hard to get on, especially for a big guy, as to make them safe they had to fit very tightly.
The advantage was that the shaft was uncovered; but the huge disadvantage as far as I was concerned is that a very heavy load is almost bound to break out.