2 problems with that method:
The toothbrush won't get the dirt down between the links and along the sides of the bushings. It will get the dirt off the sides, but that's not what destroys the chain.
I tried simple green the other day, and while it did a wonderful job on the rings, rims and the frame, it didn't clean the chain worth a d@mn. I actually had to clean it a second time, this time with the normal citrus cleaner. Don't rely on simple green for chains-it seems to be more of a detergent than a solvent.