>>1/2 dozen for me too. I switched to welding tanks as it's a much better deal. One of those benzomatic tanks costs $10 for 1.1cu ft, a 20cu ft tank swap at a welding shop is around $20.
What additional hardware do you need, such as a regulator?
How does it hook up to a plastic tube connected to a scintered stone or wand?
>> The cylinder holds 2.1 oz of oxygen. My question is does anyone know about how many 5 gallon batches I can expect to aerate with this cylinder? A rough gues is fine.
It depends on how high you have the flow.
You should not blast it, you should crack it open and let it flow at a slow rate for a minute.
If you see a lot of bubbling, you are wasting your money as the O2 will rise away and not be absorbed by your wort - unless you are oxygenating a carboy and will immediately cap it and rock it vigorously for a minute to cause the O2 in the head space to be dissolved into the work.
I have used mine for 2 batches so far, will report back when the tank is kicked.