I think the thing that's really special about Hydroguard is it has this strain of bacteria called bacillus Amyloliquefaciens. They first found this strain of bacteria in a rice paddy in Japan in the 40s or 50s, because they noticed rice (which grows in water) grew better when it was in the surrounding soil.
It seems to be pretty easy to get in Asia, but so far Hydroguard is the only supplement I know that has this bacteria in America. Root rot is caused by various microorganisms like bacteria and fungi, which can all cause similar symptoms. There are lots of various root rot products, and they all help for different "strains" of root rot, but Hydroguard seems to be the best one for the most cases. That being said, I'm sure there's some strain of root rot that is resistant.
If we could find another supplement with the same bacteria it would be great to have an alternative, especially for people outside America where Hydroguard is hard to get! I checked out the Stress Zyme but they don't explain what type of bacteria they use. It'd be funny if it had something that worked to fight root rot for plants!