The only problems on the t-case have been all on the front. I figure it's from the moment arm of the offset output. The rear doesn't have that since it is a direct in line output. If the tera low kit uses a different front case you may not have the cracking problem but unless it upgrades the size of the output shaft, that is still at risk. Mine broke on a steep hill climb where I got the front tires in the air & didn't get off the throttle quick enough.
I think the ratios of the Atlas appeal to me more for dune running. I changed gears from 4.56 to 4.88, so I really want to do a run at the dunes with the paddles & compare the current np231 ratios to see which way I should go. The other consideration is the interchangeability. I have heard rumors that when changing to a 2 speed Atlas or Stak the driveshafts have to be changed. If you do the 3 or 4 speed, they don't. That alone almost offsets the price of the multi speed box. But, that may not even be true.
At this point, I want to do a little more research. Dunes here we come!