Gents, the MK3 is a more economic version of the MK1.
3D machined 3, 6 and 9 sides
3D machined accessory rails that fit the contour of the handguard
MK1 accessory rails mount directly to the rail without using a backplate system
MK3 utilizes the MK2's accessory mounting system
MK3 has slightly thicker OD to accommodate the backplate system but still feels good in the hand due to the 3D contour