Freak
I can only speak for the freak barrels having never used the others.
It is a very good system, not only can you change the bore size to match your pain but you can change the length as well. I have the full bore set and a 16" barrel, I plan on getting other barrels so that I can create the perfect combination for the paint/field/position etc. I would imagine this would be very expensive to do with fixed barrels.
If you change your marker then all you need to buy is a new "back" section and your away again.
It also means you can use any paint on offer, as you will always get a good paint/barrel match.
Oh, and they look the b******s.
Haffa.