The $12 membrane looks die cut for the slits with a lot of wasted space for many more slits. As Bill Cody said, they look big, and big bubbles don't help much.
$36 for 3 diffusers is not at all a good deal when burning $25/month in electricity to move 75% less water....quality, effective diffusers will pay off better in the long run and even short term.
