Ideally, alternate second stages are where you stowed them when you reach for them and are not dragging along the bottom. The simple, rugged, and reliable Dive Rite Octopus Holder keeps regulator second stages securely in place when not needed, yet releases them quickly in response to a firm tug.
The elastic shock band that encircles the second stage mouthpiece does a great job of holding on to the second stage, yet will release it quickly when tugged.
The holder fits a wider variety of second stage mouthpieces than the plastic dip-molded type. You don't have to fight to get a mouthpiece in the holder - only to see it mysteriously fall out later.
The low-profile, sliding-bolt snap helps keep overall "dangle" to a minimum. It enables you to move your extra second stage quickly from one accessory D-ring to another (something many divers do when suiting up or removing equipment). It also makes the holder perfect for taming wild decompression or stage regulators.