I am enjoying my GT and Shift Kit!
There is a thought behind it, similar to Freak Inserts, however, over time the orings in the Freak Backs, can wear out and allow the insert to rotate/twist/move while firing. You have to replace the oring. Where as the Shift Kit Inserts, screw into the back it is prevented from turning while shooting.
But really - I think just about anything shoots good on the GT! muuhahahahaahaaa.
But the GT comes with a great barrel - you just need the shift kit to get the smaller bores.
Hope this helps!
My Current Markers:
(Exclusively Using Monkey Poo Lube
/ Gun Sav Lube
MacDev Clone GT
Black/Green = Ninja Air 550psi 70/4500 = Seed Rotor
Black/Green (Pooty51 Polished NDZ Can/BubbleGum Flat Face Bolt) = Ninja Air 550psi 70/4500 = Seed Rotor
Black/Green = Ninja 550psi Reg'd Crossfire 70/4500 = Seed Rotor
DigiCam Midnight (Virtue OLED) = Ninja Air 68/4500 = Seed Rotor
Midnight = Ninja Air 68/4500 = Seed Rotor
Champagne (Pooty51 Polished Bolt / Virtue OLED) = Ninja Reg'd CrossFire 70/4500 = Seed Rotor
. . BattleField Orlando