The purpose of the preventer is only partially to deal with just the wind alone moving the sail across -- you have the situation where the end of the boom gets dipped, then you have add some additional abuse as the boat starts rolling around and a slam jibe occurrs.

I think that the factors that work for the boom brake are that it eases the deceleration rather than a multipart block that "Slams" to a halt with very little "easing".

The best was is the more classic offshore method: a line led forward from the end of the boom which keeps the boom from picking up speed before it rips the stancions out of the deck or breaks the boom or both.

In reality, most people don't really sail their boat that hard -- so the boom being broken is more of a racing situation in pretty sporty seaways and winds.

By the way -- OF COURSE we all should center the boom before we jib to minimize the abuse to the sail, rig, boom sail, and/or anyone getting wacked by the boom or the sheets connected thereto. The problem is that sometimes, you get caught by either a mistake or a change in the seaway that makes your control of the situation lapse. That's why they call it a preventer. (Or is a preventOR?)