Barrel kits are subjective. If your in your early days of paintball then spend your money elsewhere
Barrel kits serve a function but are not the be all and end all
With the freak system you use a front, back and an insert to the desired size. If you have a barrel kit that uses inserts then later buy a gun with a different thread then you just get a new back to match and still use the front and inserts.
Shafts just have a front and back, when a barrel set is used where the back has the appropriate size then you buy a new gun with a different thread and you need a new set of backs
Each specific barrel set has its lovers and advantages, eg shafts may match the 2 piece joint thread of some guns which means you immeadiately supplement the standard front and back - just add the back sizes you require
Opinions differ on how you should size to match your paint, close match, underbore or overbore
