Some legit statements... I know I won't be able to stay down forever, but that little safety net the bottle provides makes me feel assured that what I've got in my lungs when I go down is not all that I'm going to have. Lowers the stress and reduces the chances of freaking out... hearing stories of others that have done the real dunker ride without any training or equipment, and how they all managed to calm down and work their way out rationally, makes me think that the bottle helps people get out period, not just gives them more time. Put air in a scared crashed pilot's lungs and I gaurentee you that the lowered fear and increased confidence they get will help him/her out quicker... not to mention give them some more air. And the bends or a possible air embolism vs. never getting out is an easy decision, at least in my mind... it's like sending someone to a gunfight without a gun because he never learned to shoot it. I think you've got a better chance with the thing, even if it's not ideal.
The instructors also stated the bottle helps you to get out, but after seeing what the bottle that I carry can do, I know I've got enough time to spend a second or two helping someone else out, or (more likely) swimming to the engine compartment to see why the damn hunk of !!!!! let me down. Even if you can't go to the class, I say get the best equipment you can afford/find/figure out how to use, get familiar with it's capabilities, and use it to it's most when the unfortunate arises...
Mike