Torsen type diffs have been around for some time, but it's just been fairly recently that they have been available in the aftermarket for the typical hot rodder rear ends. The only downside I can see to them would be that if used on a long distance road course all those gears are bound to generate quite a bit of heat. Nothing that a good cooler shouldn't be able handle. As for the older sure grips, the plate types can be set up with varying degrees of torque transfer [ tighter or looser ]. A tight one obviously is better at keeping both tires pushing. This is really good when you're going straight or nearly so. Not so good if you get too eager with the throttle since it can actually induce corner exit understeer. The oversteer has already been noted. If you can avoid the oversteer but still use too much throttle exiting the corner you can cause the front of the car to "push" off the edge of the corner. Many a novice short dirt track racer has discovered this the hard way when they shoved the front of their car into the wall. A tight diff can also cause some degree of corner entry understeer. Torsens should be free of this problem.
As for NASCAR and oval racers in general, tire stagger is frequently used to get the car to turn left. In order for tire stagger to work you have to have a locked rear end. If the amount of stagger is too great it will affect straight line speed and handling since you're dragging the inside rear down the straights.