I've been using a swimmer's snorkel for the last 2 weeks. I don't use it exclusively when doing the crawl, I'm splitting up my crawl laps 50-50 between using and not using. This seems to be a good choice. My neck is not always tender now, and when not limited by air, I can go faster, ie get a better workout for those laps. I'm still using recovery laps like breast and side stroke.
I haven't read all the thread so most likely I am repeating things here so I apologise for that. If you are getting a tender neck and lack of air when breathing, especially with crawl, I would suggest the following procedure which I learned as a kid and has never failed me in these ways you mention. When the arm is at the back of the stroke and will be brought out of the water and over to the front again, the body rocks with the opposite side entering deeper into the water, the raised arm side more out of the water and facilitating the turning of the neck to bring the mouth out of the water and air is sucked in. By the time that arm reaches the front position the lungs should be fully loaded. For the other arm no breathing takes place and the air in the lungs is released during that phase, so that when the chosen arm is again at the back of the stroke the intake of breath procedure repeats again with the stroke. Is that clear enough to understand? You can do breathing on both sides on every stroke but that is generally too much. An alternative is to intake air on one stroke, hold for the opposite side, release the air during the 3rd stroke with head kept directly in line with the spine so no twisting and then take the next breath from the other side. For instance that could be Left side breath, RS hold, LS release, RS breath, LS hold, RS release, LS breath, etc. This procedure with slight oscillation of the whole body along with the head during air intake reduces the need for neck twisting and is sufficient time for filling the lungs with air. Hope that helps, though I imagine you already know these things. Thanks for the opportunity to remember, I love swimming too!