I have both ADA diffusers and cheap Chinese diffusers. The ADAs definitely have higher quality glass, but it's really the ceramic diffuser disc that counts, and all of mine work equally well in that respect. The ADAs just do it in style. The only other thing I can think of is that my ADAs are very consistent from one to the next in terms of the diameter of the glass neck where you attach your tubing to, while the Chinese ones are all over the map. I've had some that the tubing slips off, and others that it seems impossible to get the tubing on to.