Depending on how you do them you will not fully workout the lower part of your abs and mostly the upper part. I would not do them, as you say "over regular crunches", but in addition to. In order to get a complete abs workout done you will need something like this:
Warm-up
Sit-ups, max amount possible
Workout
Hanging Leg Raises
Hanging Leg Kicks
Hanging Side Leg Lifts
Hanging V Lift
Wood Chop, High to low
Wood Chop, Low to high
Twisting Sit-up, Incline
Leg Cross Twist Crunch
Doing that once per week to begin with and you will have a complete abs workout.
Bottom line however, if you think the exercise you are doing is fun and your seeing results there is little reason to change.