The front holds up. I've only broken a stock short side inner (on Upper Heldorado in Moab) and the lincoln locker... After I broke the stock shaft I swapped to chromo inners and changed the FJ80 Birfields to 300M units:)
I do believe that if I actually spend money on GOOD gears and a locker they will hold up, but I've repaired cracks in the housing two or three times - and a few of the stud holes (that hold the third member) are stripped out.
running a Ford 9 offers other advantages. I can carry one cheap spare third member for both rigs, very upgradeable, can weld anywhere for links.
Those True-HI9's have been holding up pretty good in competition in the past two years. There was one gear ratio that's not very strong and I think that those guys always heat treat the gears also. I know that Twisted Customs runs them for everything and they are still on top...