My wife uses an H-bar on her Salsa Fargo. She loves it and I am highly considering getting one too. I've ridden her bike with the H-bar several times and if I wasn't fully in love with my Woodchipper bar I'd definitely go with an h-bar with an aero bar mounted for multi day bikepacking trips. The extra bends and area does help with lashing on all sorts of goodies. The newest version of the h bar also has a longer main grip area than the previous version which makes it easier to mount shifters and brake levers. It is pricey but very nice. My wife has the ergon grips which I also love.
The hbar does offer many hand positions and a sort of aero position but not really comparable to aero bar aero. The aero position on the hbar vs the "main" position is more like the difference of riding on brake hoods vs the drops of a road bar. I have ridden the bar with my forearms rested on both front parts of the hbar, in a pseudo aero bar position, but found the lack of arm pads to be limiting.
Compared to a flat bar with bar ends and aero bar I still prefer the hbar or my Woodchipper. Most of our rides are more than 5 hours and the multitude of positions offered by non-flat bars is quite welcome.
My wife has a brief opinion and photos of the hbar on her blog,
http://faroutwanderings.blogspot.com/2013/05/jones-h-bar-review.html?m=1