Theres some great Funco highlights in this thread. Ive owned 7 different sandcars and the only thing I would add to this thread is suspension Travel and Driver positioning.
Funco designed their cars completely around the driver making them the center point of the car in weight distribution. The balance point of my funco is directly under the rear seats (to pick all 4 tires up at the same time off one lifting point) That is, until I sit in the car, then it moves up to me. Funco's are extremely well balanced which helps them slide evenly.
Travel is another huge key point. As mentioned before, the airbag creates a unique "spring rate" that is hard to mimic and creates for an amazing ride, but the true duning factor lies in the fact that their not over stroked. Funco, in comparison, has a shorter suspension travel rate, and this is what really factors in to why they slide and turn the way they do. The long travel sandcars I have had could slide, but they couldnt slide and corner as tight and quick with out (suspension) body roll and would begin to 3-wheel through the turns. Funco's stay planted, all 4 wheels down. They can take the whoops if valved and set up correctly, but their not whoop runners. Their Dune sliders. "Nothing slides like a Funco".
Light-weight, Low center of gravity, Evenly weight-distributed, Flat surface rear tires, and a great power-to-weight ratio... can make almost anyone look good, lol.
oule: 
