I have 2 of those dischargers and love them. I used one at the last skirmish I shot when I thought I had a squib. It's too bad they haven't been available for years. They are 8 gram which was a common size at one time. The manufacturer also offered a body which took a larger cylinder as well as a flintlock adapter. You'll find, if you haven't already, they are nearly impossible to find locally and the NOx cylinders are filled to a lower pressure, don't work nearly as well and cost more. 12 gram is pretty well the standard today specially in CO2 pistols.
I have a CO2 revolver and didn't want to pay the price the airgun vendors wanted so I did a Google search and found a place to buy them much cheaper, both 8 & 12 gram. I bought both sizes in bulk (5 10 packs of 8 gram) at an almost incredible savings and I won't need any for years. Rather than waste your time and $$ do a Google search and you should find much better prices than at muzzleloading shops, eBay and Amazon.
That was a few years ago and I'm sorry to say I lost the link when I changed over to a new computer.