I don't have personal experience ordering these. However, the more popular 'chinese' ones are from Aquatic Magic. Although their workmanship can be a little sloppy, most users report decent quality for the price. But that was the thought process like a year or two or more ago, being AquaticMagic was the only China supplier who sold dirt cheap glassware compared to the monopoly we had in the US. Now I'm starting to see many options that "look" good coming from HK/China. I'd probably just choose a seller with a high feedback percentage score.
I've purchased several glassware diffusers from another chinese manufacturer called NAG-Aqua. A lot of their stuff, appear to look just like ADA & Do!Aqua but at a fraction of the price. I wouldn't be too surprised if they are even manufactured from the same sources ADA gets there stuff built (or even the other HK/China sellers for lily pipe knock-offs). ADA used to have everything made in Germany, I believe... now everything ADA are built in China. My Cal Aqua lily pipes are made in Taiwan. So I think quality has become standardized and what you're paying for is the name when you think of spending top-dollar on ADA, Do!Aqua, or Cal Aqua and the alike.