Still too wordy I am apparently, but this is interesting to me, and thinking it out, writing it out, and reading others experiences and thoughts is good for me at least. I know hearing about drysuit usage is always worth it for me. Hope you find my posts worthwhile. I know I must be repeating myself in parts, but that's because I am still thinking it all out, so some thoughts keep bubbling forward.
(First an important set of disclaimers: No dry suit diving for me. No real experience with it. That is important to keep in mind.Also students should be kept clear in the mind from divers who are done with the OW class.)
BP/Ws: They are required for all GUE courses AFAICT, and easy proper trim is the usual reason given for it. But trim can be reached in rental rec gear with proper instruction. I know because I teach only people in standard recreational gear and I have learned how to turn out trim calm divers in short courses in rental rec gear. It's not a given, but it is achievable. In that sense GUE is maybe(to a small degree) using gear (BP/W) to solve a training issue. (I am not a GUE diver or instructor.)
Arms forward is not at all detrimental for divers, as oposed to students. As LauraJ and TSandM point out, arms forward can be downright beneficial in circumstances. I myself like the pose in Sidemount because I like the tanks right under my armpits and I don't really have much choice when the tanks are in there. And for freediving, I like arms all the way forward even when I am not carry lights, because I like the full body dolphin kick.
But, arms are instinctively used on land for breaking one's fall and windmilling to regain balance. Even babies learn to run with arms forward to protect themselves, so the habit of using the arm swings to balance, and arm pushes to ward off is next to impossible to completely suppress. Students end up instinctively reacting and then consciously stifling the instinct until some other more appropriate underwater response is learned. Practicing setting buoyancy, and then doing breath pushups for a few hours starts to ingrain a new behavior patterns. Lung volume is simply never used to break one's fall on land, so there is no instinct fighting for control of lung usage*. Similarly every underwater kick is a new and different use of the legs movement, so there is no instinct fighting for control of leg movement. And full body dolphin kicks and body rotations are similarly all new tasks with body parts free from instinctive responses. If the arms are forward, students will try to use them to spin the body, instead of learning how to use the big paddles attached to the big muscles, and their abs. Or they will try and use them for balance, or to push off the bottom. Instinctual behavior can only be replaced by a more effective coping strategy, preferably with a different body part.
Arms seem to students to be useful because the arm swings to balance, and arms out to break fall are not anywhere close to a conscious response, they are a response to stimulus that precedes thought.. And simply verbally tasking a student not to use them when the arms are already forward is going to create an enormous buzz of "instinct/react to the instinct, and bite down on the instinct" chain reaction that sucks up brain cycles, and concentration cycles, and sucks away fun from diving. Instead of learning how to positively do something, they are tasked with continuously trying not to do something, which is the opposite of learning.
(Kind of like the joke: If I want you to think about a horse, they most effectively way is to say "Whatever you do, don't think about a horse". If I want them not to think about a horse, I could, should, and far more effectively, I will ask them to think about ice cream cones.)
That's jerkiness of fighting instincts, IME, is what happens when students learn with their arms forward, because 20 years of instinct is fighting with 10 days (or in my case significantly less time) of verbal instruction, instead of effective replacement body behavior. Talk is cheap, experience is priceless, is never more true than in in water scuba instruction. Don't tell students not to do something, show them how to accomplish the goal with new behavior. Anyone can learn new behavior, but unlearning behavior is incredibly difficult. Unlearning instinct withut a better more effective replacement behavior is off the chart difficult.
Experience has shown me that student divers are still in the process of trying to stop the instinctive use of hands. Putting the arms forward causes too much noise both in random jerks and such while the students goes to the instinctive response and then bites down on their instincts to stop themselves, and in the mental noise of having to keep a big "don't" flashing through the forebrain. I see these jerks in the video throughout.
Better to learn fin use and body control without the white noise of arm usage, which is still dominated by land instincts. Put the hands back, engage the rest of the body which has few instinctive barriers to effective underwater behavior. Once effective underwater behavior (and most importantly successful, positive underwater behavior) is ingrained than divers will use hands for whatever.
*Well there is but...
