Our DGX Long Neck modular valves are about { 0.4 in | 1 cm } taller than our DGX Pro modular valves, but internal parts are identical. The design of the area between the outlet and the base, the 'neck', is more accessible in the Long Neck version. This advantage makes the Long Neck version more popular with sidemount divers who find the extra neck space more convenient to use with the sidemount bungee. The squat nature of the Pro modular valves offers a lower profile that is preferred by most overhead divers to reduce chance of impact on the valves and regulator first stages when wearing manifolded doubles. However, individuals who have restricted shoulder motion may find advantage in the extra height of the Long Neck valves making it a little easier to reach back to manipulate the knobs during S-drills. The disadvantage of the Long Neck version when worn with back mount single tanks is the divers head is more likely to touch the regulator first stage. As a general rule, if neither of the Long Neck advantages apply to your style of diving then there is no reason to prefer the Long Neck versions.