Just got to L21 on 5+1 settings.
I missed the kill screen because I was stupid and trusted the hitbox on a wild barrel to be forgiving. (Argh.)
I enjoyed myself.
Oh, hey, new world record too.
One thing though: I don't understand the point of the blue hammers on the barrel board. They don't change the dynamics of the board in any way that I can discern. They're just kinda clumsy. The girder above you is too high for a jump from below to hit anything, and jumping just isn't a dynamic that you'll ever find valuable when the primary purpose of the hammer on a barrel board is to clear out barrel traffic and/or get points. If anything they're just obnoxious due to the habit we're all in of tapping on the button when the hammer is getting near expiration. (Oops, I jumped over the barrel instead of smashing it...)
I could imagine, once in a blue moon, catching a climbing fireball that you otherwise wouldn't have caught, but that's about it. I think you should just leave the brown ones.