I should perhaps have clarified: if you go for end-boom preventer to the bow, you really need a boom brake as well, for safely gybing a big rig in strong winds on your own.
The angles get too acute too quickly with a bow preventer for it to safely control the boom through the first phase of the gybe, and of course you have to switch to the main to control the second half.
Whereas with a vang-preventer, it can also be used (and should be used, IMO) to control the entire gybe. The manoeuvre is carried out quite differently with a v-p or brake vs with the mainsheet only: you don't normally bring the boom in to prepare for the gybe, unless some other considerations (like setting up the new runner, or extreme conditions of wind
or sea) dictate.
So you steer around far enough for the main to flop across while the boom stays put, and at that moment but not before, ease the vang preventer 'handsomely', surging it around a spare winch
in the correct direction (ie as if it was a sheet you had tightened using the winch
handle) to absorb the energy. You are only dealing with static forces, not kinetic energy, which makes a considerable difference.
Don't be standing or sitting on it, and don't have a loop around the pedestal
control lever! The advantage is that
(unless you've overdone the number of parts in the tackle: I've found by trial and error that two's enough up to a big-rigged 40' sloop)
you don't have much line to worry about.
If it's endless (as I mentioned in another thread which is running at present), so much the better... no stopper knots to get themselves caught in narrow crevices...
Provided your procedures are robust and careful, and the gear
is strong and well thought out and installed, I would argue a heavy air gybe with a v-p is safer than the traditional "centre the boom" method on big and/or heavy boats, particularly if they're a bit slow to respond to the helm
in big quartering seas (which includes many if not most 'traditional bluewater' boats).
That's because centering the boom before you gybe means having to manage steering
the boat within an increasingly small angular window while cranking in hundreds of feet of mainsheet, which you have no opportunity to flake before having to let it out with a rush the moment the sail gybes - a moment which is sometimes difficult to predict.
And throughout the time you're bringing in the main, the boatspeed drops and the apparent wind builds, the opposite of what you want. If you're solo, you'll have a bit on.