I bought the actual brand name Altrazine manufactured by Southern Ag. Yes, it will kill shrubs and flowers too.
I would only use it on the lawn, and try to control the flower beds some other way. I just called the manufacturer and they do not know if it will kill horse herb or not.
My primary concern is keeping it from taking over my St. Augustine lawn, which is otherwise very thick and lush. Horse herb spreads underground so it makes it difficult to fight.
Very frustrating! When I moved in, I was bombarded with Thistle. Eliminated that, even though my next door neighbor still lets it grow everywhere.
The following year Oxalis invaded. Got rid of that too! Last year when I saw the first horse herb plants emerging, I thought it was Oxalis returning. But it wasn't and the horse herb is worse and exacerbated by so many people growing it as ground cover.