I have to admit I was a little surprised to learn diquat is used in a consumer home product. Diquat is a product I use in farming, but I've always considered it to be a bit more dangerous to human health than glyphosate, so I'm very careful to use proper PPE to avoid exposure when mixing and applying.
I guess I can understand why diquat might be useful in a home setting as it wouldn't kill lawns if you sprayed some on a weed in your grass. It's also unlikely to cause herbicide resistance. We use diquat to dry down perennial crops as it does not kill the plant, and is not systemic.
Diquat is also best applied at night. I've never had it work very well when applied during the day, so that's another reason I'm surprised it's in a consumer weed spray.
I've heard of farmers using acetic acid (vinegar) as an alternative to diquat, and it apparently works quite well, but it's quite a bit more dangerous than diquat as it can burn skin and lungs easily, and it's very hard on machines.