I have 5 Great Northern bow quivers. The small size arrow gripper is what I use for MFX and Axis arrows. The medium size will not grip them at all as it is too large. Additionally, I use the small size for Traditional Only and GT shafts as well as the medium does not grip those shafts adequately/securely either.
The great Northern quivers are fantastic quivers. Well made, quiet, durable, and they keep broadheads safe and secure, shafts tightly gripped, and with adequate spread of the shafts to prevent fetching contact.
Go with the small gripper.