Many of our customers feel that an enclosed track speargun is quicker to reload than an open track speargun.
Also, the enclosed track barrel of our guns allows the use of an open muzzle. Some people feel that an open muzzle provides better visibility and aiming or sighting of the target. With an open track and an open muzzle, the shooting line needs to be wrapped over the shaft at the muzzle in order to secure the shaft prior to the shot. This entire step is eliminated with an enclosed track because the shaft is secured by the track.
The enclosed track ensures that the shaft leaves the gun straight and that it is not whipping or bending. Many people feel that the enclosed track will allow additional band power to be used. This may be true to a certain extent but the mass of a gun limits the number of bands which are practical (without generating excessive recoil), so the realistic limits for our rail guns are 2 or 3 bands.
The MAKO Spearguns enclosed track barrel incorporates two additional extensions of aluminum which are used to anchor the polymer track. This pipe was designed specifically for our use and is extruded as a "custom" tube. This provides additional rigidity to the barrel.
We have also heard from several customers indicating that they feel that the shaft being cradled in the polymer (enclosed) track also serves to reduce the sound of the gun. We've never quantified this effect, but it is also a potential benefit. The polymer track is resistant to wear, provides a low friction surface and is easily replaceable should it be damaged by accident.
We sell both open track and enclosed track spearguns, however we do not offer any models in CF... we should mention that since the original question pertained to CF versus aluminum.