It works fine.
I used to have my VP150 mounted above my screen in v2.0 of my theater as seen in this picture using a single FMB:
The tricky part for me was that I was putting the speaker as high up as possible (under some ductwork) so my big monkey hands had a tricky time getting everything mounted, but it was doable and surprisingly solid.
Of course, mount it to a stud. There are a lot of shear forces pulling on the bolts you use.
For v3.0, I ended up putting the VP150 on a shelf below the screen since there was room, and in v4.0, I am using a VP180 on a shelf behind the (new) screen.
M60s,VP180,VP150,QS8s,20-39PCi,DMP-BDT210,HD-A2,JVC RS45, Onkyo TX-NR709, Shakers