I recently got a V Force reed block for my 2010 YZ250, I didn't notice/feel any increase in power. On the dirt-Track I did notice it did seem to fall flat on top quite soon; I might have a play with the inner plastic guide which could be a little restrictive maybe?
Some website forums talk about removing the reed block spacer for more top-end but I am thinking the reed block would then restrict the rear transfer port.
I do agree with the fact that, with double the reeds, they won't have to open as far, hence they should last longer.
MXA seems to rave about them, they tend to say "get the V Force for midrange and the Rad Valve for top end".
What bike you want to put it in?