axle-mounted rear ders?

[Windbreaker]

I've been seeing in some of the bike mags mt. bikes are now coming with "axle mounted rear deraillers." What are these? What are their advantages and disadvantages? Does anyone have a pic of a rear-der mounted on a bike?

I'm truly curious--thanks for indulging my n00b question.

 

[free_rideman]

They are made for the downhill/freeride types of people. I think only shimano does it right now, with their Hone, and Saint groupos. They do this to tuck the derailluer up and away from harms way, and thus not having to worry about a derailleur hanger. They say it is supposed to be cool and everything, but I could care less. I think it is more of a marketing scheme, since now you would need to buy either a shimano saint/hone hub, with the special axle thingy, or some others companies hub. Sometimes some hubs can have a adapter axle for purchase to accept these weird derailleurs. Which again, costs more money.