I was told by a landscape gardener that Burn Out II was relatively benign. It has clove oil, citric acid, and sodium lauryl sulfate. However, this gardener also thought Round Up was not a big deal. I did use the Burn Out and it worked fine, and my hope is that she is right about it being relatively benign.

There are some weed situations where hand pulling is very difficult or has a really low success rate--in cement cracks, in gravel, etc.---when you can't get the root out. I expect that's why the OP was asking.