I don't have a clue .... they don't sell them here in the UK (I have to order from the USA) .... but from what I have read on other forums from guys who do long/ultra distances, these are really good and used by many
I've read that too. I've seen pictures of them and thought they were leather cover over padding and (I assumed) and stamped steel seat pan but that looks like leather formed and tensioned between the front and rear frames. I've not been able to find a picture of the underside of one of those.