I find the more channels we have the more we split our membership, or feel required to join a bunch of channels. I like the idea of a place to organize and host achievement runs, but I think doing that through pickup groups formed on the forums is fine. Any groups formed in CTRLFG are always welcome. The benefit to using CTRLFG is you end up with more people to potentially help you get the job done. I know it's hard to find people to do achievement runs, why make that exposure any smaller when searching for people? You never know when someone who doesn't normally consider and achievement run will decide it's what they want to do that afternoon.
I would say keep using CTRLFG, you get more people seeing your posts about a group. Use the forums, get the word out there in advance. Try forming an achievement team, make a schedule for what you are doing each week, get it out there and see who signs up.