I just installed a Wavebox into my 300G.
I also have 2 each 6100s. Bebo77 is right, the Wavebox is a nice compliment, but should be thought of as a replacement to powerheads.
I've heard of some folks complaining about clicking noises, etc from their Wavebox, but I've not experienced that.
I like the Wavebox because it creates a nice and RANDOM motion in the tank. A powerhead alone, no matter how it is controlled, still provides a stream of water in one direction. You can stop and start, increase and decrease the stream, but a powerhead still provides the same general push of water.
When you combine the Wavebox and streams, you get a nice random effect across the tank. It's like sloshing around a bowl of soup while stirring it with two spoons.