Soo ... I repeat why hasn't "everyone" been using helium instead of hydrogen all along??
On the surface,it seems like a no brainer for absorption refrigerator manufacturers from day-one to have been using helium. Unless, as Chris mentioned, it's helium's higher partial pressure that kindof made it, or makes it ... a show-stopper ... and that Atwood is really taking a chance on adequate product performance by using helium this far along in the history of absorption refrigerators.
I still think absorption refrigerators are an absolute genius invention and perfect for drycamping RV use - especially if RV manufacturers would mount them on a gimbal mechanism (which I would pay the extra $$ for) so that they were always level no matter what angle the RV was at. ;)