I used siporax for many years in my old setup...
I had an overflow chamber about 6" x 6" x 18", in the display tank, which had a 2&1/2" down-pipe, for the full height, so I filled the area round it with the siporax, and covered with a few scourers that I could replace when they got dirty. The theory was that there would be eddy currents in the siporax, which would be enough flow to allow for denitration to occur... And any trapped sulphurous gasses would "burp" out without causing contamination to either the tank or the sump!
'Fact is, I NEVER got any sulphur smells, so I assume I got it right, and after a few years, I eventually gave up monitoring nitrate, as I never got a reading!
The tank was set up for about ten years like this, but I did also have a DSB in a sump as big as the display tank, which may have had something to do with that too!
In that time, I emigrated, and the display tank was obviously scrubbed back.
The siporax had a period of six weeks in a shipping container, for the move but was boiled, then Micro'd to remove all debris and was transported in a loose cloth bag, prior to being set up in the new location, where it was left to cycle for a good few weeks (with a new DSB) before any new stock was added.
I love the stuff: I think it gives an extra line of defence in the battle against nitrates, but $500 worth of the stuff? I think I'd go without!