I have a walder boom brake (similar to shown - but not exact) and swear by it. Indeed, as a risk management tool against, hard crash jibes, head injuries etc. this is cheap insurance at around $500. Many folk prefer restrictors, but my view is they are harder to set up/manage/control.
With a 50m2 main , I have mine set up around mid boom, with line back to a 4:1 block next to the helm.
It takes a bit of practice to work out the right tension (based on friction through the screw type pully), but as in my case, I can use it like a handbrake and make fine adjustments depending on wind strength.
Result - no more unexpected jibes & very controllable mainsail movement either tacking (softer) or jibing.
More importantly, my wife and kids love it!
