I have one. You need 30 (more like 40psi) for it to work. This means WORKING psi. DiY yeast can NOT make this pressure. You need to dial up your regulator's WORKING PRESSURE for this thing to work. Yes it works wonderfully too.
There are two gauges on your regulator. One is tank pressure which is normlly 1100psi and the other is working pressure which ranges 0-100 psi. Most diffusers work on only about 10 psi. You turn the nob in the middle to make it go up. Do this VERY slowly or you'll blow the gauge.
And the GLA diffuser is WAYYY over priced. You can get it elsewher for around 20 bucks online. I had a friend pick one up for me when she visited hong kong for only about 15 bucks.
And yes the GLA diffuser is just a repackaged UP aqua diffuser that you see on ebay. The shrimp lab also sells them for a lot less. Many of these "high class" plant stores are rip off stores. I'd steer well away from them... (unless you're getting a tank or something...I'd want assurance that there won't be 30 gallons of water on my floor)
The same EXACT thing (same manufacture etc.) at the shrimp lab:
30psi is not a quantity of co2
but a force of it coming out of your needle/metering valve. Bubble count will ballpark your co2