I picked a few of these up since they're so cheap. I now have all of the compact lights I'll ever need (until the Amaran MX ships and then I might need one or two more)...

Anyway, I haven't put it next to an M9 to check the brightness, but the GVB light is pretty bright. It seemed a little brighter to me than I remember my M9's being - which would make some sense since it has 12 lights to the 9 on the M9. I think I also like the GVB shoe/tripod mount more than the one that comes with the Amaran. They end up taking about the same amount of space in the bag, but the GVB one is a little more flexible and should be easier to replace if I lose/break it.

The GVB may also survive better during prolonged use, especially in warm areas - it has more ventilation holes in it.

Absolutely unimportant difference: The Amaran M9 comes with a piece of tissue paper (for additional diffusion), a warming gel, and a cooling gel. The GVB only comes with the cooling gel.