Having used a denitrator with 4 gallons of LSM, I'm not really concerned on the toxic front. For one thing, if this was an issue for this application we would be seeing warning labels up the ying yang, and would have confirmed lawsuits from the US. If that was the case, I doubt that Caribsea and Korallin would still be marketing their products ... too much liability given our litigious nature (ever notice how many warning labels are on ladders these days
).
I'll definately concede that for industrial settings, this can be serious stuff. However, Delbeek and Sprung devote 7 pages to sulphur denitrification, and only a couple sentence mentions of hydrogen sulfide smell as an issue, mainly around the ambience impact of a smelly living room. The chemical reaction from Holmes-Farley shows:
2 H2O + 5 S + 6 NO3- ---> 3 N2 (gas) + 5 SO42- (sulphate) + 4 H+ (hence slightly acidic effluent and the reason for calcareous material after the sulphur)
so no H2S is emitted in the primary reaction, unless the flow is too slow and secondary chemical reactions occur. As you mention Tony, the 1 ppm level will provide ample nasal warning before the level can rise to dangerous levels (which I doubt is even possible ... as this application has been used in Europe for over 10 years on some massive aquariums).
Also, with a recircuation system, the volume of sulphur would be much less than even I'm using.