question about hyperventilation

this weekend I was watching the PADI OW DVD with my girlfriend who is getting certified. In section 4 or 5, they talked about free diving and using hyperventilation to lenghten the the time before the desire to take a breath while snokreling or free diving.

now I understand the concept here, lower the current co2 level thus lengthen the time until the co2 level stimulates the urge to take a breath and I also understand that we do not use all of the o2 in our lungs so it is a way to "trick" ourselves into not feeling that urge and use more of the o2.

my understanding of how shallow water blackouts sometimes happen is by the time you feel the urge to breathe, the o2 gets too low and you might lose consciousness. I also thought there was another type of blackout that happens when the ppco2 is increased when surfacing and that can also cause a blackout but I cannot find any reference.

I also thought that apnea divers look down on this practice, preferring breath hold and muscle training.

so here is my problem/question, is the introduction of a potentially dangerous practice a good idea for new divers especially because they very lightly covered the science and dangers behind it? and am I right or wrong to mention this to my girlfriend and suggest avoiding hyperventilation all together while free diving?

My own method of hyperventilating before a free dive is to take no more than four deep breaths, then hold the fifth one. For me, this allows me to stay down longer without causing any problems with the urge to breathe.

I teach students to take 3-4 deep breaths, holding the last one for their skin diving skill. In the briefing the "benefit" given to them is: You are snorkeling either instead of diving, or as a surface interval, you have your camera, see something cool, it is a way to get the shot without waiting for the next dive, but be careful, water changes depth perception and don't over breathe."