The comfo-bite is branded and patented by Aqualung so you won't see any support from them or Atomic on using that mouthpiece.
The Comfobite is meant for Apeks which have a larger orifice opening than the Atomic, though the Aqualung regulators share the same orifice size as Atomic. 21/16"x11/16" for Apeks, 19/16"x10/16" for Aqualung/Atomic. That won't really make a huge difference, but it makes it a little easier for it to freeflow.
Now, the point is it freeflows at the surface. That means one of two things; that your tech is a knucklehead and tuned it too sensitive, which is a common problem; or, more likely, you have the venturi lever in the on position and the adjustment knob turned all the way so it makes the reg prone to freeflowing. Either way it needs to be backed off because a freeflowing reg due to purge is dangerous, especially in cold water diving, but also in an emergency situation. The regs should only freeflow when turned diaphragm down when they are full of air without a mouth on them. I.e. hit purge button underwater with the mouthpiece up, or take the reg out of your mouth underwater and turn it mouthpiece up before it floods completely.
As this is the Atomic subforum, they will tell you to use Atomic mouthpieces only and I'll probably get a PM saying it's an Atomic forum and we shouldn't be suggesting other brands stuff, though I might escape unscathed since you already have it on there, not sure how the Atomic guys are, I know the Aqualung guys get real fiesty.
Edit: not implying your tech is a knucklehead, but it is quite common for shops to tune the primary regulator so cracking pressure and WoB is almost nothing, and while it is nice to have something breathe that easily, there is a balance point so they won't freeflow when they aren't supposed to.
