Tim,
A Choke design that has a parallel section, whether your talking a fixed choke or a choke tube, will pretty much always produce the densest long range pattern, especially with larger shot.
This parallel section needs to be longer, the tighter the choke constriction is. Thus, the parallel section in a Full choke needs to be longer than said parallel section in a Modified choke.
A parallel section in the choke system means a longer choke than most times found in a conical one.
So, the longer choke tubes are more of an advantage for tighter chokes, longer distances, and bigger shot.
For the skeet shooter, using a skeet choke and #9 shot at 15 to 25 yard distances, it probably makes very little difference if the choke tubes have a parallel section of not, and thereby the longer choke tube with a parallel section versus a shorter conical one has no real (or big) advantage in that application.
For the hunter pass shooting ducks at 50 yards with a Full choke and size 4 KTM or Bismuth pellets, the longer choke tubes with a parallel section will be advantageous.
Hope this helps.
