Short Answer: Kinda pointless I've seen Sprouts give better advice as well as play better than the vast majority of CM players
Long Answer: I love the idea of this. Players who put themselves forward to offer advice on either how to play better or the ones to explain tactics on bosses when things go wrong. It seems however in reality this never happens. Sadly every time I've met a CM it's been a negative experience. From a CM tank on Odin who despite 3-4 people saying they are new went and insta pulled the boss and even after 4 wipes refused to say anything, to most recently having a CM healer in my dungeon group who was telling me I should be using my Storm's Eye ability as a warrior a lot more often despite the fact he was so bad at healing I was having to pop pretty much every cd I had on every pull just to stay alive as he did pretty much nothing but spam damage spells.
I've been told a lot of players just have the CM icon to get the free goodies that comes with it. That saddens me as it feels like it tarnishes what was supposed to be an awesome way for people to help and be looked for when someone needed help.
Now of course I might just be super unlucky with the ones I've met and the majority could be those super awesome people who do help. Please tell me if that's the case!
I just wanted to put forward my experience with combat mentors as someone who at the time of writing this has 722 hours in game (A scary amount of that is levelling up my gathering professions)
(The two experiences I put aren't the only two I just didn't want to bore people by recounting every single time I've met a CM)
As a final point I know this is rather negative post but I do want to make the point that 99% of players I meet in game are awesome it just seems out of that 1% of the not so nice bunch that a lot are CMs