I get why Cho'Gall doesn't have mana because the hero would be unusable otherwise (even with 2 separate mana pools), but I'm not sure the CD's on his spells are in the right place. Cho's feel too long and Gall's too short. Gall's Shadowflame is 1 second shorter of a CD than Murky's Slime (3 vs 4) , while 2 of Cho's abilities are 12+ seconds.
Cho's impact just feels pretty weak compared to Gall. His fist ability is clunky and doesn't seem useful unless you heavily talent it (but why would you when the other options are so much better). The aoe flame ability is better but not great, although it becomes a very powerful defensive spell with talents. The end result is that Cho doesn't really have much to actively do other than pressing Rune Bomb for Gall and moving around so Gall can cast his other spells. It feels like if you split them up, Cho would be trash, but Gall would still be good.
Time will tell of course, and most games are skewed by the fact there's a Cho'Gall on each team. With a 5 man team vs a Cho'Gall it's much easier to counterplay in my opinion, but when you have 2 running around things are just chaotic.