Sorry to jump in, but I used a FMB to mount my VP150 when I first set it up. Worked fine until I moved my theater. Seems pretty solid actually. The biggest issue what that I was mounting everything to fit under a soffit that was there for duct work, so I had to cram everything as close to the ceiling as possible and it made messing with it a bit tricky just to get it mounted the first time.
I put it above my screen back then:
After that, when I moved into a different room, I just made a little shelf below the screen. I liked the way it sounded a little better too. Picture is dark, but you can see it under the screen (it is on a shelf, trust me).
And now I have a VP180 on a custom built (yeah, that means DIY) stand that is behind by current screen so that it is in line with the tweeters of my front mains and directly behind the main part of the screen where it should be. Picture below was before I took down the screen to install them.
But yes, the FMB can successfully (and without concern) hold a VP150.
