You want to buy mine?
I'm actually pretty dead set against them for a couple reasons.
Cost is big.. 18 sites x $20= $360!!
You can't use just a couple of them on a splitter. They are really tight and air will flow to other more porous stones
They make the pump work harder
There is less air flow, yes the bubbles are smaller but overall, compared to the sheer number of bubbles coming off the blue stones it's really close.
The biggest reason..in a 40 gallon res, one 4" blue stone was able to provide max DO
They are high quality and very though. Not going to break them and reusing then is a plus. I think if you just need a couple might be a good investment. I need a total of 42 stones though for 18 site veg room and 12 site flower (With 2 stones each) . Thats more than $800 for a one time investment. That's equal to replacing the blue stones 20 times...which is 5 years worth of grows. I probably won't be growing in 5 years.
But anywho, many ways to skin a horse.