I tried out the BK3 and the Mezz PowerBreak Pro with the H shaft.
Really loved both of them. It's not the standard feedback you get with most cues when you break. Almost feels as if you're hitting slower through the cue ball. Best way I can describe it is that it feels like the cue is playing "catch up" with your arm speed...like the amount of time spent with the shaft on the cueball is longer than usual. I don't have any scientific evidence to back any of this up, but it definitely feels like you're transferring more energy.
I ended up going with the Mezz, but the BK3 is right there. Feels light when breaking, and it's very easy to get a good spread without having to break as hard.