There is no proof that Excel is somehow safer than Metricide.
Yeah, I know. That's why I said 'a bit safer'.. But there are no studies on it.. Honestly, I've stopped using excel.
Further, this "glutaraldehyde" derivative is an unknown compound. Seachem said years ago that they would elaborate after getting it patented, but was unable to secure a patent. This leads me to believe that it is nothing more than a diluted version of Glutaraldehyde, just like Metricide.
Actually it is known, I saw the name of it but it's so long, I've forgotten it.. Something like iso.....glutataldehyde.... But as you said, it's still under the patent procedure so they can't release their method for making this compound.
Metricide is NOT pure Glutaraldehyde. It is diluted and continuing to perpetuate that it is somehow some nasty chemical and Excel is like bottled water is both irresponsible and false.
It's not pure glutaradehyde but it doesn't mean it's safe. There are scientific papers on the negative effects of it in the environment, water notably.
Either way, use excel or metricide at your discretion.