They do boost the O2 level, though it's less than originally
thought. The help with circulation, especially in areas which might be
hard to reach with an outside filter. They break up the surface
protein layer and help re-oxygenation at the surface.

I can't agree with you more on breaking up the surface protein layer. I
had a kinda ugly layer before I added the air-wand to my tank. No trace
of it now:-). Also the fishes seem to enjoy swimming through it, and
floating up in it.

Josh