I had one in the front of my '71, until my last trip to Moab. Functionally, I never had any problems with it. It was smooth and I never had a problem getting it to lock up, even with one wheel in the air. However, they aren't very tough and, sadly, it couldn't take two full days of slickrock.
If you aren't looking for hard-core performance the trutrac is probably a good choice. At least there aren't any clutches to wear and there isn't a need for additives in the gear lube. I was able to drive it on icy roads with out too much difficulty. I just chose not to most of the time.