Homebrewers - Whats in the fermenter?

One-Step is basically the same thing as OxiClean, just with a different base material to make it easier to work with. Sodium Percarbonate becomes a weak hydrogen peroxide solution in water. This does well with cleaning and but only OK with sanitization.

If you look at the packaging, One-Step never actually claims to be a sanitizer. They can't since they have never proved that they meet the FDA required levels of sanitization. I got some One-Step with my first equipment kit, so I used it for cleaning until it was gone, but always followed up with Star-San as a sanitizer. After it was gone, I just used OxiClean Free. One benefit to this is that you're using an alkaline cleaner, then following up with an acid sanitizer, so it's a more complete system.