I used the Crown CM-311A for two decades, loved it! First and foremost, it provides me with the freedom I did not have with a handheld mic on a stand. I could move anywhere and not worry about the mic position. The footprint was relatively small, especially in comparison with a handheld mic and I never had to worry about feedback while using the Bose sound systems. The range of the CM-311A was very short and the difference between full vocal sound and no sound coming through the mic is just the difference of positioning it so the mic touches your lips (per the instruction manual) and no sound at all was just moving the mic head a couple inches to where it was below your chin.
The sound quality of the CM-311-A was nearly as good as my Sennheiser E855. When properly positioned, there were no breath sounds and the frequency range was superior to nearly every handheld mic I ever owned. The clarity was superior to the Shure SM-58 and equally as good as my Sennheiser.
While you could not utilize the mic proximity effect, vocal control easily compensated for this, though some here may argue that point. Dozens of top entertainers used this mic and it was designed for Garth Brooks. It is also used by Sher Bono, Madonna, and many others.
While it is not as comfortable as some other headset mics, it's really not that uncomfortable, and after a couple weeks, I really didn't notice this unless I had to do a 4 hour job with no breaks. And, I too wear eye glasses.
Now, as UD said, I dead plugged my onboard speakers while using the Bose line array systems. When the speakers were positioned off to the side and a bit behind me, I heard exactly what the audience heard. There was no need for monitors. Additionally, using the onboard speakers as monitors can pose a problem, which I discovered the hard way. I had a job one day where I arrived just two minutes before the job was to begin because I got caught in heavy traffic. When there is an accident on I-95 and you are no where near an exit, everything just comes to a dead stop. I called the AD and she said it was not a problem.
Upon my arrival there were about 200 people waiting in the auditorium at Pickeresgill Retirement. They were all staring at me, or it seemed that way, while I was setting up as fast as I could. Back then I used to leave the onboard speakers turned on. Well, I fired up the keyboard, began playing and singing and noticed that no one seemed to be paying any attention at all other than a few folks in the first row sitting a few feet away. Then one got up and came to me and said, "something must be wrong, we can barely hear you." I had forgotten to switch on the Bose, but didn't realize it because I could hear myself just fine through the onboard speakers. That never happened again after dead plugging the onboard speakers.
When I used the CM-311A as a wireless mic, I used the Samson Wireless system, which has a tiny transmitter about the size of a 12-gauge shotgun shell. It plugs directly into any XLR connected mic, and fit nicely on the Crown beltpac. The range was incredible and I never had a problem with it. Later, I want to direct wiring because it eliminated more things to carry and that could possibly go wrong.
Hope this helps,
Gary