Siaokao sounds like a true blue tekkie there, The environ kit sealing the 1st stage has more to do with Cold Water Diving, Dirt being secondary. By preventing the influx of water into the 1st stage, you prevent the risk of the water freezing up the reg, stopping the functioning of the 1st stage and essentially cutting off air supply. Whether the virtues of the environ kit applies to tropical / muck diving remains to be seen as the benefits might be outweighed by the (unnecessary) cost (servicing, parts, etc).
The Scubapro comes from a reliable lineage rivalled today only by Aqualung (aka. US Divers), co-founded by Jacque Cousteau in 1943. If you're only thinking about rec. diving, don't fret too much, most regs do the job well.