Hey man, by any chance are you a leftie ?
That darker patch on the plus 12k just some heartwood, which is a harden wood and is nothing wrong with it. Its basically a stronger part of the wood, some pros love it on the outside of their bats when driving and cutting (apparently less prone to cracking) and obviously if the ball hits that part will go further. Even if you right handed and like the leg side its probably handy to have, people get silly about it because its not as pleasing on the eye !
As for the 8K its grains are wider (again no proof in what I'm saying but iv heard a lot of club players at my team say this) but apparently the bat last longer with wider grains. Short and narrow grains don't last very long, but bigger wider grains do.
Both bats look great, tbh iv got a ca as well and they look very similar to each other. Id say tell your brother what exactly you want from the bat i.e. wight ratio and edge sizes and go with that. Both bats look fantastic and i can't really say 1 is miles better than the other, the new design of CA really stands out. As for that pre knocked sticker. DO NOT LISTEN TO IT lol, your bat will crack, oil and knock it in for 3-6 hours minimum. I don't know WHY CA put that sticker on its not knocked in at all !!!!
(Side not check for back profile of the willows) the larger the concaving the narrower the sweet spot, the less concaving the wider the sweet spot. GOOD LUCK with either bat i hope you score a bucket of runs my friend !
