I have sort of.
Mucinex is my go to drug for my sinuses and allergies. Whenever I'm well hydrated when I need to take it, I've noticed increased cm when I've had to take it, not even for ttc reasons at all.
I've been a little sick with allergies recently and have been taking generic, but haven't noticed any changes. However, I've also not been keeping very well hydrated, and that makes a huge difference.
If you do decide to give it a try, make sure guaifenesin is the ONLY active ingredient. Some cough medications have other active ingredients that could actually dry you up.
I don't know how well you do with keeping yourself hydrated, but it's absolutely essential for cm regardless of using guaifenesin or not. The hydration is what will increase it, but the guaifenesin is what will thin it out. But if you're not hydrated enough, it probably won't make much of a difference (such as in my case).