To paraphrase a certain British Intelligence agent with bad teeth...
Allow myself to explain.. myself.
This is what the normal gearstick movement is for selecting second gear. Across, and back. Nice and easy.
The black circle shows the maximum available travel of the gearstick in the standard mount assuming it wasn't connected to the gearbox. as you can see, all gears can be selected as they are within range of the gearstick's maximum travel.
Now let's look at a cross section of the Compbrake style quickshifter..
The locking collars of the gearstick (which aren't present on an OEM gearstick) contact the underside of the billet mount and limit the total movement of the gearstick. If you move the fulcrum of the gearstick too far, the movement of the gearstick is limited so much it has an affect on gear selection, as per below:
As you can see now, limiting the movement of the gearstick means the natural resting position of the gearstick in gears 1, 2, 4 and 6 (or reverse) is compromised. This means the movement of the gearstick to select a gear has to curve at the end of its travel (blue arrow in pic). This means the gearstick is resting in an unnatural position when in gear, and the lateral load ie, the difference between the natural resting position and the new resting position (shown by the green arrow) puts pressure on the synchros of the gearbox and may well cause premature failure.
Correct adjustment of the assembly however should have no ill effects on the gearbox.