I used one for a couple of months and was happy with the performance until....
First of all it's murder trying to find a replacement airstone (one made of that wood) that actually fits. Trying to shave one down is a lot of trouble and negatively affects the limewood.
It's also degraded in performance as it's become encrusted with algae and such , and even with regular cleanings it still seems to have pooped out on me.
I just replaced it with a prizm and I have to say that this thing pulls out so much more gunk that I don't know why I ever went the cheap route to begin with. I've got 2 prizms and I love them both- a little noizy though.