Both are good barrels (I've got em both
) but with the freak you have the inserts that mean you've got 6 barrels to do that with a boomy would cost 2 or 3 times the cost of a freak kit and as was said you only need the back if you change marker. I use a Cocker and an Impulse both on my freak I have a full kit with an extra back and front for the other marker so both are ready to rock
seriously though barrel kits are the way to go and their are some good ones out their my advice is a Freak kit.