I have been looking at boom brakes and was quite surprised by the cost of them. Anyone have any opinions on them.

Have you used them and what do you think? We have one that came with our 'new' boat.
I like the idea but the main already has a lot of friction and it doesn't want to feed out when you go downwind- you have to push it or 'unthread' , feed out loose mainsheet. I'm thinking a boom brake would compound that problem?
We haven't had the boat out in much over 15kts as it hasn't blown much since we got it 6 weeks ago so maybe the boom will go out a bit better in strong winds...( without the brake).