Well, it's a bit bigger than the Lumiquest one - about 14"x18", I think. It diffuses plenty if it's close enough, and if a little further, keeps the texture to the fur, I find. I try to keep them set to almost unnoticeably add light.
Really, it's a matter of keeping your subjects small, and getting the boxes as close as possible - the mantra I normally go by is, "If the lights aren't almost in the way of the shot, they're not close enough." Anything larger than small children, and I go to a shoot-through umbrella with the Sb units. Saving pennies for an Alien Bee 800, likely that will initite my downfall to full-size strobes. Below, one with pal's kids with the softboxes and Speedlights...
