I am not comfortable with the vent-frees either. There are plumbers in my area installing those things in bedrooms all the time. I can smell the emissions and can see the moisture in rooms where those are installed! I believe code here allows them in non-bedroom space, I don't like them in any living space. Mayber a garage or an unoccupied storage space. And yes, I don't blame you for wanting to be able to come up with a solution to avoid purchasing glass doors, but still provide the safety of an open damper.
I just read a great book on the very effective and functional fireplaces that Count Rumford designed in the 1800's. Shortly after he designed his fireplaces, Ben Franklin designed the "Ben Franklin woodstove", these closed metal stoves became so popular that fire place use and design development quickly became extinct. Not many people have given much thought to designing and building functional fireplaces since before Franklin. That's why so many modern fireplaces are terrible at burning a clean, hot fire, and why so many of them don't draft well and often send smoke back into the room. The old Rumford design from over 100 yrs ago is one of the only designs that considers these issues and solves them. He was simply forgotten by time and other innovations. But with the number of people who want fireplaces in their homes, they should take the time to consider his design.
Molo