Hello, I'm the inventor of the above Free-Fall harness hook.
I've read what happened to Jose and can only wish him to recover completely.
I have a french client who broke his neck (but never got paralyzed) while speed training (fin). He now has 2 titanium vertebras...
His head struck the mast when he fell at high speed because of a loose fishing net...
When you fall feet over head an hooked in, it all depends on how you turn. If you turn sideways (most common) then you twist the line. But if you turn facing the sail then your upper body ends up inside the boom. Depending on the length of the line and the sail position your head may get stuck on the mast or boom. A helmet will help for the head but will not protect the crush on the spine in those cases.
If well tuned The Free-Fall Harness hook will open during the fall and should thus prevent this sort of danger.
Of course, the better you ride, the faster you go, and the more energy there is in the crashes.
I have read this topic from the start and seen also concerns about backlash. Building up neck muscles will indeed be a good idea but I think a big helmet can help also. It should of course be as light as possible but what is important is its surface. A big helmet will stop on the water while a small (or none) helmet will not stop the head on the surface.

At this time I'm using a cut DH helmet (Kenny) in which I replaced the foam on the cheeks by some that won't take up water. (easy needle work)
It is 750 gr and seems to do its job. I feel my head against the back of the helmet when I fall and my head doesn't go as far back as before.
As it is a DH helmet it is well suited to use with some sort of neck brace. I will see this winter (this fall...) if I feel it is needed.
I have kept the cheek parts but I suppose I could make it lighter doing some more extreme cutting but I have manage in the past to catch the mast on my left cheek bone...
My previous helmet was 400 gr but didn't prevent backlash... And it was black which should be prohibited as nobody in difficulty will get noticed in the water with a black helmet.
I won't be producing helmets ( I already do safety foostraps)... So if any brand could take my reflections into consideration and come up with a 400g big and flashy helmet, it would be great.
Brands definitely should take security into consideration. Selling fast stuff is nice but safety gear is needed.