I think the HDC is outstanding. We used it a lot when descending steep snow covered trails in Ouray / Silverton, Colorado area. With the HDC on and the autostick in 1st gear I don't think I could walk down the trail any slower than the GC was going. In 1st it will go no faster than 1mph, 2nd gear 2mpg and so on through 4th. Always felt very sure-footed.
My trail only Jeep Scrambler with 4:88 gears, 4:1 low range and (can't remember 1st gear tranny ratio off the top of my head but low) will not descend as slow as the GC.