Again I understand completely, and I understand the arguement for one.
However I think one that vents to the low side, and have designed the unit with a static pressure that works, is 1000x better then a release of ethylene (and possibly liquid ethylene) into your work area. After having tested a few types of pop off valves they don't psssst, at least mines don't, they just blow, one was insanely loud too. If no ones around or a units outside, sure, perfect, but for a cascade like ours I think its not an appropriate safety measure.