Hi Deepthought,
I don't think you get hypothermic at the surface before the dive. Numerous studies have shown that cold adapted people (swimmer Lynn Cox, for example) actually see a rise in the core body temperature after initial immersion and vasoconstriction. In our experience with no-suit diving, it is easier to relax in colder water (after the initial shock of getting in subsides) despite the fact that hypothermia will come on faster.
It is not obvious to most observers that it is far easier to relax in water colder than 10C (once you get in, of course
) than it is to relax in water in the 14-20C range. In the warmer water, shivering can start after your second or third dive, which makes things rather unpleasant. Problems with diving in colder water (for me, anyway) are head freeze and groin freeze, although after a few sessions, these tend to go away. Once on a very long recreational dive I had a wickedly fast onset of narcosis (feelings of doom) and I was still on my way down at around 25m.
On a single deep dive without any water warm ups, hypothermia is minimal compared to a longer no suit diving session. I think the most I've shivered after a deep dive is 20 min, whereas after a much longer session 3 dives, 2min+ each, I'll shiver for closer to 40 min - 60 min.
As far a competition goes, no suit diving is beautifully simple. No lube, no worrying about your suit tearing, no nausea, no overheating, no sweating inside the suit, and you always feel ready to go down without a suit on, whereas many times I've felt that the suit is keeping me from being in dive mode, insulating me from the water. Also, the freedom of being unencumbered by a suit is sensational.
The deepest I've gone without a suit is 45m and it was the most enjoyable competition dive of my life (I cut my depth at the last minute because of chest congestion).
I suppose the only disadvantage to no suit freediving would be in more tropical waters where there are stinging jellyfish and sea lice.
Pete