Hey Dyer and welcome to the Shack!
The BFD will definitely handle your feedback problems... that is of course what it was originally designed for and it does it automatically.
I'm with Phil on the bright room... turn the lights down... or wait til the batteries run down.
We have a problem in our fellowship hall with really bad echo since we remodeled it. We took the lowered ceilings out and dressed up the original cathedral ceiling. Plus we took the carpet up and installed ceramic tile. All walls are sheetrock. If you only have about 10 folks in there you can't even talk and understand each other. We are in the process of getting some heavy drapes to go over the side windows and plan on building some frames of insulation and covering them with the GOM material. We'll place them all around the room.
You might post a question about this in the Custom Installation forum and see if you can get some more input.